The long-awaited (and much-speculated) return of Sandor Clegane finally occurred in the Season 6 Game of Thrones episode "The Broken Man." With him serving The Faith and The Mountain about to rep Cersei in a trial by combat, fans are wondering: will The Hound kill The Mountain?
Well, for now, his ties to The Faith may be cut. Though he was rescued by a retired soldier-turned-monk, who operates a compound of people most closely resembling an AA commune, that compound was ransacked by the Brotherhood Without Banners. The Brotherhood come looking for supplies, but The Elder Brother claims he has nothing to offer. The Hound warns him that he has food, lumber, steel, and women, which is plenty to be stolen, but The Elder Brother ignores his warning.
While The Hound is out chopping firewood, he hears screams coming from the compound and goes running back, only to find everyone dead, including The Elder Brother, who is hanging from the structure they were trying to build. Sandor Clegane grabs his ax and walks off, though it's not exactly clear where he's going.
Is it possible he'll find his way back to King's Landing and find some way to face off against The Mountain in a trial by combat anyway? Sure, though his ties to The Faith and whatever he felt he owed The Elder Brother are now severed, since his rescuer is dead. He seemed more energized than anything else to go after The Brotherhood, who had captured him and Arya once before, and who clearly recognized him as The Hound when they visited the compound.
The Hound doesn't exactly have lasting loyalties; he mostly seems to go where the stability is and serve there. But he does have a lasting grudge against his brother The Mountain, and being free of The Elder Brother might just motivate him to pick Cleganebowl — as it's known to fans — back up again. It's widely speculated that the two will reunite on the show in a battle that favors The Hound, who was horrifically facially scarred by his brother during a childhood fight. Having his face shoved in a fire by The Mountain as a boy gives The Hound plenty of motivation to go back and fight him, even if where the episode leaves him doesn't make his fate totally clear.