"I do not mind; I was in the Halls of Mandos, where I thought I would dwell until Dagor Dagorath, and the end of all things." Fëanáro gives his new companion a wry smile, and continues, "Not that I have any objection to being freed of that prison before that time."

If indeed it is before that time; it could very well be that he has been released only to watch the world burn as Morgoth Bauglir returns.