I had this fic idea literal seconds after I woke up:
Fic where Arthur from RDR is seeing demons and stuff and thinks he is being punished, so low honor route, and maybe he hints at it slightly to Reverend, but he gets attacked one day by one and turns out Dean and Sam from spn are stuck in the past and trying to get back w/ a powered down Castiel.
Castiel probably talks to Dutch and that could be interesting because Dutch is so far off the deep end with his ideals like Cas was when he became a god.
Lonesome Dove crossover part:
Maybe Woodrow Call from Streets Of Laredo makes a short appearance and Dean sees him settled down (he was a very accomplished bounty hunter and ranger). Dean and Sam see what life could be like but Dean feels it’s hopeless and Sam is beginning to lose hope. Call might talk about Gus a little and Dean can see some parallels between him and Dean, but ultimately thinks that Gus is more like Sam. Less ties to duty, but would do it if he had to for Dean or someone they care about. Dean has Gus’s indulgence but Call’s.. well, call.
Note: I’ve only read Lonesome Dove and Streets of Laredo. I’ve finished both RDR games but no online stuff or Undead Nightmare. Also, I’m on season 8 of spn.