User blog comment:AVP3/Final Episode of Adventure Time/Adventure Time Movie/@comment-1992701-20130807061048/@comment-5829421-20130808024049

Even if Betty survived the mushroom war, (which is already incredibly unlikely) she still would have died of old age, so how would she still be alive? Also, since the crown is what's making Ice King insane, and it's the thing that's keeping him alive, if they destroyed the crown in order to make him sane, it would kill him.