If true it would be awesome - much more of a living world.

Suggestion way back was to have dynamic lairs - over time they grow and spawn critters, more powerful as time goes by.  I think this kind of made it in.

The other was to have a zone of control that mobs attempt to protect.  As they grow in above the zone of control also increases.  When the game is first created you would have overlapping zones of control and if mobs ran into each other - they'd fight.   Strongest survive.  If the evolution of the lairs reached a point where one zone overlapped another lair they might try to clear the lair/maybe even capture/use it.

Darklings probably wouldn't get too far, but even a slow spawning (nastier mobs spawn slower) dragon or hoarder may take over lair or two.