ToME: the Tales of Maj'Eyal

I have tried this with two characters, same result.
When trying to leave the Dark Crypt after saving Melinda, I get a lua error regarding an attempt to gain the achievement.
It records the quest as completed first, but the only way out is to kill Melinda, which resets the quest to failed.

This is due to "achievement" being misspelled in zones/crypt-kryl-feijan/zone.lua line 109. Its been fixed in the SVN but you can make the fix yourself if you don't mind playing with a bad game version.

The file I'm editing is in
"t-engine4-windows-1.0.0beta23\t-engine4-windows-1.0.0beta23\game\modules\tome\data\zones\crypt-kryl-feijan"

But the problem persists. Is that where I should be looking?

Or is the zone file loaded into my character folder already (I have a save on the stairs out), leaving me no real options unless I want to start a new character (which won't have the same problem if I've made the edit) or fail the quest?

If you're already in the final crypt zone, then changing the file won't help. You need to cheat a different way

First, enter cheat mode (search forums for directions). Once your character is loaded, you need to enter the Lua console by pressing [ctrl]-L (or maybe [ctrl]-A, I can't recall for certain). Then, simply type "game.zone.on_leave = null" (without the quotations, of course). Also, you should do this after you already tried to exit in order to complete the quest and get your reward.

This worked for me, so if it doesn't work for you, then I probably mistyped something. Good luck!