Board Thread:Off Topic/@comment-216.65.166.241-20130808065946/@comment-6881629-20151129142422

Followers shouldn't be able to go to Skuldafn, if they don't appear when you return try waiting or fast traveling. If their left alone for so long though they will dismiss themselves and return home. There is a chance something goes wrong and the follower might glitch and get lost, so it is a good idea to take them home and dismissing them yourself before they get left on their own too long (from quests they can't accompany you on or just making them wait).

If your on a PC you can return to Skuldafn using the commands mention on the wiki pages trivia section here (but again a follower shouldn't be able to go there), or try and recover the follower with the commands (change refidhere for the ref id code on their wiki page) -

prid refidhere

moveto player