If you miss mindreading Ragnar in the bandit camp (ie before reporting the location to Louis), the only thing you are missing from behind the gates is Jagon's diary and some lowish level random loot.
There is nothing useful on the roof, at least that anyone has reported finding. I tried to get through there somewhere in the original release; if I remember my next game (in the Developer's Cut version) I should try again, using the teleport cheat function.
