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>>716507041
The original ending for 3 involved having Sonic end up in a "bad future" somehow and showing that Robotnik survived (also those storyboards that leaked before release showed a different ending for Robotnik's "death" where he gets sucked into a time warp). They probably shelved the sequence when they couldn't cement Carrey coming back for a fourth and left things intentionally ambiguous instead.
I guess this confirms the fourth movie will be about time travel nonsense.