"You should have faded by now."
"It's hard to leave when you haven't said goodbye."
"Then tell me, because I don't know...How do I say it?"
"If you ever loved me, say it like you're going to come back."
"...See you around Professor River Song."
"Till the next time."
"Don't wait up."
So this is kind of my final homage to Eleven and River. I don't know if Moffat will ever bring her back, but even if he did, it wouldn't be the same without the floppy-haired cutie.
Also, I feel like the fact that River gave him all of her extra regenerations probably played a role in the fact that he was able to regenerate again into Peter Capaldi, but that's just an opinion.
This idea has been rolling around in my head for a while now, but I haven't had a lot of extra time.