actually, probably he died when he failed to hotwire the car, and everything after he sits back up is his dying fantasy

everything happens that way because that's walt's plan, in his head, unfolding in his head in the perfect way he imagined it, as he drops the keys and cops surround his car

norm macdonald's theory about the ending is correct. the machine gun thing, his speech in his ex-wife's house, all the fantasy of a sad, dying man