He told me to meet him in the map room in the throne room of kings. The only problem is that he isn't there! I helped one of my friends with the quest and saw where he was; I even had quest help on and it was pointing right where he would have been standing.
I even tried logging out and back in, but still no Professor Winthrop. Could this be fixed? I really want to progress further into the game...
Sometimes things don't load right. You should still be able to walk up to the point where the NPC is supposed to be and see an interaction prompt. If not, it may need to reset, which could take up to 60 minutes for a dungeon or instance.
The dungeon should reset if you exit through the same door you entered. Try going back out, changing realms and entering again. If you still don't see Prof. Winthrop, go to where he's supposed to be and press "x" anyway, see if he's just invisible.