Moff has said when The Ponds leave it will be a tearjerker... i don't think he is implying death, i think he's implying that they will turn around to The Doctor and say "we've had enough". thats the vibe that i see building over these first 3 episodes anyway
I'm expecting an ending similar to The Time Traveler's Wife
-- the Doctor doesn't see them again for a long
time, and then he sees Amy for the last time on her deathbed, decades after they last traveled together.