Well, I have not yet finished the outpost/town/dungeon, but we did start running it this afternoon. Fortunately, the PCs failed to notice the orc guardpost at the top of the knob above the outpost, and entered via the back door of the keep (which had once been hidden but was now exposed due to a collapse in the covering/sheltering rock. Deep below, the orcs are now set up and ready for intruders at any time. In fact, the orc shaman is hoping - justifiably, if the PCs keep going the way they have been - that the intruders will wipe out the undead in the uppermost levels of the outpost, and then he/his folk can rededicate the dwarven temple there to their own Beast Lord in the future.
I think that the orcs will send their women/children away in boats across the lake to safety, and then attempt to bargain with the intruders/PCs and find out what they want here. If possible, and if the PCs are not too violent in their reaction (I don't know HOW the dwarf wizard PC will react to orcs in a one-time dwarvish hold), they'll make a deal to let the PCs pass through the lair, deeper into the outpost, down to where it connects to deepearth, leaving the orcs alone. If the PCs agree, of course, then if they come back this way, and they're not looking hale and strong, the orcs will break whatever promises they've made.
If the orcs and adventurers can't come to an agreement, I'll have a nice running dungeon battle between about 50 orcs, a war-chief, a shaman and his apprentice, 2 orogs, and a few wargs, versus 3 6th-level PCs and a 4th lvl NPC.