I really hope something timey wimey is going to happen with River as well. Something positive. As for the Doctor trying to undo everything so that Amy and Rory can have Melody, I can see that happening. But it would change a lot of things. It might even make it so that her name isn't Melody, and that Rory and Amy never got together. But if that happens, I'm sure it won't be that drastic. I definitely don't think River would be okay with that.
In A Good Man Goes to War, I was under the impression that the reason River couldn't come until the very end was because she couldn't interact with her own time stream. But seeing as she is in the astronaut suit, there will be two Rivers in the same place at the same time.