Montagu should be at the back of the slayer camp, on the first level up, near the entrance that leads to the door to the prison teleporter, but not in the alcove.
Svadilfari should be friendly when you first approach, but can turn hostile then (depending on your conversation options), or later.
If the troll runekeeper is missing, you can still proceed if you have the Developer's Cut version of the game:
Totally stuck in High Hill troll cave.
