User blog comment:KillRoy231/My review of the Deadly Six/@comment-477304-20131021001503/@comment-477304-20131021101112

The event happened in the past (well technically in an alternate future), but I think the explosion could be treated as non-canon, as Metal Sonic appeared in Sonic 4, and that game shows that Metal was revived after the battle at Stardust Speedway. Even if the event is treated as canon, Metal is a robot, Eggman can simply build another one, in fact, there's not way to determine if all Metal Sonic's appearances are the same robot.