ToME: the Tales of Maj'Eyal

In my previous playthrough, I did that "trapped" quest and it didn't occur to me that I could talk the lord and lost merchant and ended up killing both of them. Will they respawn in my next playthrough or are they gone for good like the escorts you can send to Zigur?

They occur for every playthrough. Just like the escorts (which aren't 'gone for good' by the way).