Let's look at an example:
<WillRespawn>0</WillRespawn> -> means it will not respawn after you kill it.
<WanderingRadius>0</WanderingRadius> -> means it will stay and guard the lait.
There's also a tag present in some lairs that on influence hit it will release its guardians who then go roaming. Like this: <ReleaseGuardiansOnInfluenceHit>1</ReleaseGuardiansOnInfluenceHit>
The below regulates respawn rate (chance, delay) and wandering radius of the spawn monsters.
And here's en example of lairs upgrading:
<UpgradesToGoodieHut>Lair_DeathDemon</UpgradesToGoodieHut> -> and that GoodieHut (Lair) will then spawn the monsters defined for that.
I hope this helped a bit .