Depends on a bunch of things, primarily how much Chaos itself is focusing on you. Right now they're primarily focused on stomping humanity/'good' races since that fits their preferred narrative, and chaos are really big on narrative, especially in daemonic forces. A Khornate chaos lord, for instance, might be smart enough to do a siege, but a khorne daemon won't do that pansy waiting stuff. So if you repel whatever attack might be coming Hell Pit's way, they might respond with bigger forces or they might just brush it off, depending on how exactly you repelled them/poked the metaphorical bear. Sorry I can't give a more specific answer, but think of it like this: Karak Dum was able to survive in the warp for 20 subjective years despite being repeatedly attacked by daemons because that fit their narrative of being really fucking hard to wear down, and often in the warp or warp-saturated areas like most of Norsca narrative matters more than fact. You could exploit this even, though I can't think of a specific way to do that at the moment. Daemon-related stuff would probably benefit a lot from that type of environment though. I'll mention that the norscan daemons seem mostly to be khornate at the moment, though.