I don't know how loud I can say this but
TIME TRAVEL DOES NOT WORK THAT WAY!
No matter how often you claim big timey wimey ball you cannot just try to resolve your writing fumbles with use of it.
To whit:
We know for sure shooting fact that River Song died with the tenth Doctor David tenant in her future, the doctor's past, aving met and married the Doctor at a later point in his current timeline.
This means that River Song cannot die now, because it means that No. 10 will never have met her, meaning No. 11 won't trust her in the same way that he did because he had previously met her as No. 10, meaning that the entire events of this season would be thrown into nonsense by the rewriting of history. You can't just change stuff like that.
The only other option to choose is that River Song does not die, the Doctor does not die, and clearly the universe cannot have not existed (Unless they want to claim that they are just undoing all of the Doctor Who continuity for no real reason) meaning there is very little dramatic tension. We know he must succeed and that River must live because they have already met in the future, meaning that there must be a future otherwise this future could not have progressed as it did.
The only tension is whether Amy dies, which frankly I don't care about from a longer term time travel story point of view (sure emotionally her death would suck, but that's not the issue). I love Steven Moffat, and after he went so far as to coin the phrase 'big timey wimey ball' I thought he understood time paradox a little better tha this. This is a weak storyline with no tension behind it because unless they end the series with the universe utterly destroyed then we already know how the problem is resolved.
I could write a better time travel story than this, and mine suck.
