Is the quest "Avid collector" fixed with this 1.20 patch? The bug where the bookseller is nowhere to be found and the quest remains unresolved because of it?

Try a reload... the bookseller should be there.

Reloading, reinstalling, exiting, whatever... doesn't work. He's just physically not in the shop. Nor anywhere else in the vicinity, although the quest marker is firmly planted in his shop.