For example, in the Caverns of Thracia I don’t really have much more than a general sense that “the cultists control this chunk of the map”, “the lizardmen control these rooms”, “the anubians are based out of this complex”, and the like. Most of the time, it’s not necessary to get really obsessive with this.
Who can take advantage of that? What will the Orc King’s response be? Actually, wait, they killed the Orc King. It can largely just be a matter of keeping one eye on it during your restocking process: “Okay, the PCs killed 70% of the orc population on Level 3. Nor does this have to be something that you need heavily pre-plan. (And even moreso if these factions are openly hostile to each other.) This becomes even easier if the dungeon contains multiple, independent factions. The life of the dungeon will naturally generate the ideas necessary to restock the dungeon (and, thus, carry a lot of the weight for you).
To immediately boil the idea down to its core: If your dungeon has a life beyond the activities of the PCs, it is much easier to revitalize the dungeon between delves. Now I want to build on those ideas by touching on the basic concept of factions in the dungeon. In “ Wandering Adventures” I talked about how the OD&D wandering monster tables could be used to generate entire adventures.
In “ (Re)-Running the Megadungeon” I talked about how to keep a dungeon complex fresh by restocking the room key and using wandering monster tables as a form of low-tech procedural content generation.