The only place where that's gotten sticky for me is Region F. The party had a tough time there, and what little they knew of Region G scared the bejeezus out of them. They were all for heading into Section E and an easier challenge.
What most of them didn't realize was, of course, was that with the party around 9th level it was going to be much
too easy. I didn't want to get heavy-handed about steering them away, but I was sweating. I did explain the layout of the dungeon to them, and one of the players correctly deduced that Region E was roughly equivalent to Region B, and pointed out to the other players that they'd get bored. They ultimately went for Region G, and are currently going through absolute hell.
While looking at my options, I did decide the Region E was manageable. The "border" encounters are close enough in challenge rating to be at least interesting, which is a nice feature throughout the dungeon. The map layout also made it likely that I could subtly steer them up into Region I, which would be a reasonable (and creepy) challenge for them. Finally, you've got the "how to upgrade" listings in every encounter, which I would have used if they'd been hell-bent on going deep into Region E. Overall, not that big a problem, and yet another reason I Like This Dungeon.
(For what it's worth, the party's path so far has been: A, brief trip to E followed by fleeing in terror, B, C, back through B up to a nose-bloodying war with the two tribes in F, now off to G where the ladies are giving the PCs what-for.)
cheers,