ToME: the Tales of Maj'Eyal

Is it possible to clear the relevant dungeon without getting NPC alchemist's elixir ingredients that are only available there?

For example, I think I've killed everything in the Lake of Nur and the Maze, but I'm missing the Pouch of Luminous Horror Dust.

Should I go back to these areas and pick them over carefully for hidden rooms or did I just get unlucky?

Thanks!

PS
I'm new to Maj'Eyal, but not to roguelikes. Really enjoying it so far.

You'll see more Luminous Horrors the future, don't worry too much about missing them for now. The only ingredients I ever miss completely are Wyrm ingredients.

The monsters are (mostly) determined randomly; if they don't spawn in an area then you can't collect the corresponding ingredients. Try to go further, Luminous Horrors may also appear in some vaults in other zones.

elixir ingredients aren't guaranteed to find

Some critters including dragons, undead and horrors can spawn in Farportal realms, so that's a decent last resort for some of those.

Every Adventurer which tries to ambush you on the world map each have a 30% chance to drop a random ingredient on death.

Some critters have special zones (mummies for example), other special zones (naga, ritches) will be revealed when you travel for plot.

Thanks guys, that was exactly the information I needed.