ToME: the Tales of Maj'Eyal

So let's say I cleared out Trollmire at like lv8, but I didn't encounter the troll wizard. Can I never get the Rune now?

He can spawn randomly in other areas even at higher levels,
also, the rune can spawn in rune shops sometimes.

Anywhere that trolls can spawn in.

You can also get the rune as a random drop from whatever enemy, but it's more rare. I even found it lying on the ground once.