Unless you guys really suck, a battle of this size should go down in less than five minutes. Taking into consideration how long it takes to stab someone to death, and applying a bit of tabletop, I'd say that if you guys can take out the surface guards after the away crew leaves, you might have a few minutes to deal with the last few in the ravine before the away crew could arrive, assuming they could even tell something was going on. Otherwise they'd leave without ever knowing their HQ got sacked. Though depending on how you do it they may or may not be aware of your presence. It's not a deep ravine, barely large enough to hold the the ferals in cages while giving space forthe robed man a private room. Bandits sleep outside just so ya know.