Do you honestly think they'd kill a character off-screen and never mention it?

Also, she's mentioned in Frontiers, mentioned in TMoStH, appears in Dream Team and will appear in Crossworlds.

@KillRoy231

One of the many Death Egg robots were found on Chaos Island, so we know that his influence has indeed stretched the world. (Could be possible that very robot reported back to Dr. Eggman leading to the events of Frontiers.)

No, but I would like to have an idea of where she is at least so I know for sure. (I like to think she is not dead, and if they make more sequels to Frontiers she might appear sooner or later, but just curious as to her absence without any mention of her just so we know). When asked about characters absent from the final episode of MLP: FiM, Jim Miller said "Just coz they're not in the finale doesn't mean they're deceased." Except Granny Smith, to which he said "No one lives forever."

Crossworlds is irrelevant because Fun and Games like those, Mario Kart, Mario & Sonic, etc. are not canon. Just for having fun racing or playing minigames as your favorite characters.

Although the real reason is that Cream isn't that popular, but my guess for her absence is that she is staying with her mother Vanilla for safety.

Probably. That's what I'll go with, they're safe somewhere until Eggman's defeat.

@KillRoy231 There's no reason to assume spin offs like that aren't canon. Team Sonic Racing was explicitly stated to be canon.

It's common knowledge. Do you think the Mario Kart games are canon? Mario Party? Mario & Sonic? Super Smash Bros.? There's no way Super Smash is canon. These games don't have a story to them (except Super Smash Bros. Brawl and Ultimate, each telling their own independent crossover story), or consistency with the mainline games. It's all just fun and games, a way to play races and minigames as your favorite characters.

Sonic Riders games and maybe Team Sonic Racing have a story to them so they can fit into canon. But the Free Mode races with characters like Blaze and Shadow in Zero Gravity for instance aren't canon, just the main story modes. Unless Crossworlds has a story meant to fit into canon, and honestly I'm not sure that Mario Kart style games need one, they're just for fun.

It's not common knowledge at all, it's an assumption you've made without evidence.

It should be pretty obvious actually. Do you seriously think Mario and Sonic characters canonically cross over in London and places like that? And Eggman, Metal Sonic, Bowser, and Bowser Jr. in more friendly competition and sometimes on the heroes' teams?

I mean, if you want to headcanon it, go ahead, but don't speak for the rest of us.

We were doing so well, why start now?

Mario and Sonic is a rare exception and I didn't bring up those games. What should be obvious is that the majority of spin-offs are canon and there's nothing to contradict that they aren't. You're just making the assumption for no real reason.