I really think Micah is Rebel. Anyone who's skeptical based on his age, obviously don't remember anything about the character. Micah was extremely intelligent and much wiser then the average kid.
I don't doubt for a second he could pull it off. I actually had the thought before I saw this thread.
I think the Molly theory is very plausible too. That could explain how Rebel was warning everyone in advance. Micah could perceivably do this on his own but knowing the Heroes writers i wouldn't be surprised.