I'm afraid that this isn't something I feel I can confine to just a single paragraph or two, so bear with me -- I'll try my best to explain my reasoning. Let's begin:
So basically, you feel that if a former Admin has done nothing to tarnish their reputation before taking a leave of absence that has extended to the point of them their losing their rank, that said User not only technically still has the same reputation they've had since they were active, but as a result of this line of thinking that you also believe that it should constitute a quick and easy way for said User to regain their former rank should they decide to ever return? To be honest, I don't really agree with that interpretation.
Depending on the time span of the leave of absence in question, a person's skills/personality traits/etc. can change quite a bit from around the time they leave to when they decide to return. For example, let's say you decide, for whatever reason, to take a leave of absence from SNN for, say, half a year, maybe more. During this timeframe we could get a decent number of new Users who'd be unfamiliar with you on a personal level, both professionally and not, and all they'd have to go on, if they feel so inclined, is to look at your past contributions to the Wiki and your interactions with it's community members during the time you were active here. From the period you've left until the time you return, these newbies would most likely have nothing to go on when it comes to who you are as a person in this hypothetical scenario, since I doubt anyone but whom you consider friends on here, people who already know you and vice versa, would have any reason to try and keep in touch with you (assuming you were to allow any of them to do so.). If I were a new User who joined up 6+ months after you left and all of a sudden I'd see you, a former Admin/Crat show back up after a prolonged period of absence, I'd be curious and cautious of you because, while I can understand and respect your past achievements on this platform, your past deeds from half a year ago or more would do little to nothing on their own to prove to me that, in the present, you'd still be as reliable and hardworking now as you were then.
Allow me to also cite myself as an example: there was a period of time in recent history where my range of activity around this Wiki began to decrease, and the amount of work I had no problem doing on a semi-regular basis became something of a chore to me that at many times I found myself lacking sufficient motivation to do, because at the time I was going through personal issues that were making me mentally fatigued in nearly all areas of my life, and affecting my general performance/attitude in these areas as a result. Due to these issues I was facing, it was not uncommon to see me entirely absent from the Wiki from many days to weeks on end, and barely doing any work at all during the times I did log on, preferring to talk rather than do anything else save for what I felt was absolutely mandatory for someone of my position to do, such as enforcing the rules, deleting spam articles, etc.. It was only little more than half a year ago that I've taken care of most of these personal issues of mine, and am in the process of trying to deal with the residual effects they've had on me and my overall performance in various areas of my life, but even now I'm still struggling with a few things both in and outside of this Wiki, and even though I'm trying to keep myself open to community input about myself I realize that in some areas I'm still not performing as efficiently as I used to before my personal issues began to affect me as badly as they have, and I have no idea when I'll fully recover from them either. In other words, due to circumstances in my life that have all but made me take a leave of absence of my own (because, again, with how I was at the worst of it, I might as well have been a ghost to the majority of SNN's User base that choose occasionally popping in without warning that more often than not barely had the mental energy most of the time to even care much over anything that was going on with the Wiki at a whole.), I've not only undoubtedly affected the perception that the people here who knew me have had of me during this time period, but I've also created a situation where many of the new Users who were joining this Wiki at the time barely had time to interact with me, and only had the words of other people who knew me to go on in terms of who I am to this Wiki, along with my past accomplishments, and even then I've already pointed out how even that perception those who knew me had of me was likely being soured in some level due to my changes in behavior.
I know that pointing out how my personal issues affected my perception of how anyone here who knew me is by itself ultimately irrelevant to this line of inquiry, but the reason I bring it up because regardless of the context behind my changes in behavior and how it's affected my performance around SNN at the time, there were several Users who were joining up at this time who I know knew little of me on a personal level, and frankly, from then to even now, I don't fault them if at any point they've ever wondered what exactly was so great about me that warranted me obtaining the rank of Administrator at some point in the past, when during that period of time I was barely present for much of anything on the Wiki at the time. If I did have to require my Admin rank through a vote, assuming that I never got my rights back after I had lost them (Bluespeeder restored them on his own when it became clear that I was becoming active again.), what reason would these new Users have to believe that I'd use those tools as responsibly in the present as I did in the past? If I were in their position, I'd know what I would've thought: none. And if I were to have inquired with any of the older Users here about this former Admin and have discovered underlying issues they were having with this person due to various changes in their behavior and how these issues have related to their overall degradation of performance around SNN, it would make this former Admin look even more suspect in my eyes and it'd increase my skepticism of their ability even further. I very likely would've at least stayed neutral on the issue, if not flat-out vote in opposition towards them getting their rights back, because again, given circumstances such as these, what reason would I have to believe that such a person would be as qualified to be an Admin now in the present as they were in the past?
I know I'm kind of rambling a bit, but you do understand what I am saying, no? While I myself, if persuaded sufficiently, would be willing to at least consider giving a person like this the benefit of the doubt regardless of the reasons why I'd feel hesitant to vote in their favor, that doesn't mean that anyone else should, or likely would, feel obligated to do the same, because at the end of the day I do believe that a lack of proof that a person in the present is just as reliable as they were in the past is a pretty sufficient reason to be hesitant to give just anyone who had a good reputation in the past an easy ticket to regaining their former Admin rights.
But on a related note, last time I checked, a former Admin who has had a good reputation with the Wiki before leaving for whatever reason would actually potentially have a much easier time regaining their former ranks if they can demonstrate within a reasonable timeframe that they can perform much of their former work in spite of the limitations brought upon by being a non-Admin, while also showing themselves to be capable of interacting with the Wiki's community members in a way that closely, if not precisely resembles how they used to interact with other members on here during the time when they were active. Basically, show themselves willing to work as hard as the community feels is necessary, both in managing the content around the Wiki itself and how they interact with the various other members of said Wiki, in order to earn enough approval from said community that they are most certainly deserving of a quick and easy ticket to regaining their former rank(s). At least on paper, this means that it's possible that such former Admins won't have to work as hard to regain their former status on the Wiki, assuming that such a rule is never modified/expunged for whatever reason, and in practice I've personally never seen the few instances where I've witnessed a former Admin returning having to go through a great deal of trials before being given these easy tickets to regaining their rights -- they've usually been able to get back on their feet without too much issue. As such I personally have no issue with this rule existing, as I'd expect people on here to want me to prove myself to them before they felt comfortable letting me regain my rank(s), should I have lost my own rank due to a prolonged leave of absence, just as much as they'd expect the same for anyone else in this position to do the same. In my eyes, it's pretty reasonable.
So, no, ultimately I don't think that we should change this rule.