Same issue here. It is my only main quest objective as well, so I cannot advance in the game. The wolf will not resurface.
I really enjoy the game, unfortunately there are far too many bugs to put it on my list of recommendations. I can't even finish the game cause theres a game breaking main quest bug that is not letting me advance.
Fenrir stays underground and will not come up. This is the only main story quest I have right now so I am STUCK and CANNOT advance any further. This needs to be fixed yesterday.