>>102769526>Finn being in some alternate world or something where Jake was just a normal dog>with a 2D guy and he wished for a sandwich
Yeah, that all happened, it was the beginning of season 5. (I had to look that up because it's been so long)
Everything is being blown out of proportion as always. They had to fit a lot into it so characters other than Finn and Jake get focused on, but they're important in the climax too.
They didn't die, but the epilogue and framing device is set thousands of years later so technically most of them, the mortal ones, died at some point.