He is claimed by another.

[Through The Living Ash he/him]

I'm pretty sure the book describes Dalinar as slipping through Retributions grasp until he was gone, which seems clear that he passed into the Beyond. Cultivation is definitely the most likely one to have claimed him before he passed on, with the amount of meddling she did with him. With the ability to see exact replicas of the past, it is theoretically possible to bring someone back even after they passed to the Beyond, though it would be extremely difficult. They could never be exactly the same, but they could be really close. Kelsier was the best example of how this would work, though he still existed as a Cognitive Shadow.