(This is perhaps somewhat freaky and kind of AU, but...oh well. Might as well throw it out there.)
After his death, Jim (or rather, his soul) waits for Spock's katra to join him 'on the other side'. But when several decades have passed, longer than what most Vulcans could be expected to live, Jim finally start to worry. He returns to the mortal plane as a ghost, and somehow finds out that Spock's katra is being held in a katric arc in the Hall of Ancient Thought. Jim frees him, somehow- either by himself, or with the help of someone (a psychic human or Vulcan, for example) and he and Spock rejoin each other in the afterlife.
Doesn't have to be a long fic, I'd just be very honoured if someone who has more time and writing chops than me gave this a try :)
, Fiction Characters: Original Character(s)