Re: How will the Ponds depart?
I still like the idea of The Doctor saying goodbye for a time and pledging to return but botching the time period and coming back after they've died of old age. It would be different than any of the other conventional DW send-offs and thematically appropriate because it would make Amy still "the girl who waited."
"Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying."
--Arthur C. Clarke