POV switches! You noticed! :D And yes, it was a deliberate decision to put the final goodbye firmly from her POV, because as you say, in context, it's such a sadder, more tragic moment now we know her story. I think it's always River saying goodbye because River is the one, at this point, with knowledge. She knows who she's saying goodbye too. The Doctor is still at the point where she drops in and out of his life like a whirlwind, but we're following his POV, so River says goodbye to us too. It'll be interesting, I think, if we ever see a situation where the Doctor knows more than River and has to say goodbye to her.

OH RIVER. <3