After searching and searching and only running into dead ends is his search to save Dean and Cas, the switch in Sam finally flips.

He's not evil, just powerful, so powerful. He tears open Purgatory all on his own and pulls them both out, only them, nothing else escapes. Dean's thrilled for about a second before he realizes what Sam's done. Forget the Lucifer damage, Sam's powers, now unable to be shut off again, have destroyed his mind. Taken everything down to a single goal, get Cas and Dean, save Dean.

Dean and Cas reform their mismashed family, supporting Sam and keeping him safe.