Hey,
I'm stuck in the quest "Now or Never" (where you help Triss and the mages flee Novigrad) in the sewers.

I went trough the library, where I had to blow away the walls, and though the two-storie room with rats at the bottom. The Corridor after that has two doors: one up the stairs and one strait ahead. Both are locked and I can't see another way out there.
The walktrough I consulted at eurogamer mentioned nothing about closed doors. Is this a bug, or did I forget something?

Picture shows the exit of the rat room, with the locked door and stairs to the other one.

The door at the top of the stairs is the way out & should be unlocked if you have cleared the rooms before it.
Try closing the game & this time loading a save from an earlier checkpoint & replaying this part of the quest see if the door is open when you reach it

That did it. Thanks! :)

i managed to get pat that vampire thing at level 10 without fighting the vampire thing but now me and triss are stuck in the room where your supposed to fight it so help! do i have to fight it?

I did that too, I forgot to take Triss. I felt like a complete idiot. XD