Amy will discover she's pregnant (having been cured by the miracle doctor in "A Town Called Mercy"). She won't want to travel in the TARDIS in case this baby also develops a "Time Head". They'll go home and live happily ever after.
River will get sent back in time by the Angels, set up home with Casanova and neatly avoid all that inconvenient prison stuff. She reckons this is a better deal than living in jail and 'dying' in the library.
The Doctor will be forced to accept their choices, finally realising that companions are people with independent will rather than toys to be played with. He may actually do a bit of growing up and become more of a Time Lord and less of a ADHD kid (or at least more like he was in other regenerations).