Or Amy, who is the apparent sole arbiter of what can or can't come back based on what she remembers, ended up remembering Auton Rory Who Guarded Her For Almost Two Milennia And How Fucking Devoted Is That You Can't Get Any Better And Besides He More Or Less Has Original Rory's Soul Anyway, and the universe shrugs and makes things work out in the background.
What really creeped me out about the episode was that i was EXPECTING some of the 'here's me from the present going back to the past and doing this thing' stuff that happened- and yet the rapidfire of it took me so by surprise that I missed the 'oh yeah, I knew that'.
I'm fairly sure River will turn up before we get 12. Whether it's a River who's contiguous with what we've seen of River is anyone's guess.
Yes- why the cracks, who controlled the TARDIS, who said 'And in the end was silence' (I think that's who you mean by the voice?). I don't doubt Moffat will do as good a job making it all make sense as he did with this season.