There might also be a chance that if you keep going forward the other characters will warp to you for the next segment when you need more then one. There are a few places like that in some of the levels. At least you helped find one of the odd bugs in the game.
If you have the monk in your group, you won't miss his section. The minor differences in the cave are there to make sure you can't pass a section for one of your current characters and that you can pass any sections that you don't have the characters for.