The dude at Quiet Isle doesn't really answer Brienne's question about Sandors death. He only says, that "The Hound" is dead and Sandor "at rest".
Also Sandors horse "Stranger" and that really huge man (the gravedigger) are both there.
This and the fact that Gregor is probably not dead already (and has to be killed) makes it pretty likely that Sandor is alive as well.
Of course all this could just as well be trolling by GRRM.
Still this would be my favorite besides Jaime beeing the Valonqar.