So I was fighting the academy students in Qara's quest outside the Sunken Flagon and my lovely gnome decided to put "Charm Person" on Ashni. As a result he now just stands there and as I cannot defeat or interact with him the quest is on hold. This appears to be permanent. Is there *any* way to reverse the effects of this charm person spell? It has happened a few times in battle, though only on wolves or unimportant monsters. I know this doesn't strictly matter as I'd rather have Sand in my party but as an OCD gamer it can be pretty tricky.

Dispel Magic.
Have you tried resting?
As a last resort, you could try:
pause
right click on Ashni to target him
debugmode 1
dm_setfaction hostile
debugmode 0

Thanks for your reply! We're half way there. I managed to get Ashini hostile but none of my attacks can harm him, I get a list of 0s. I will try to find a solution but this code will be useful, thank you!

He is not meant to die, when his health is low enough, Johcris is meant to show up.
You could try this from KevL.
http://forum.bioware.com/topic/505320-oc-script-bug-in-qaras-quest/

Sorry to necro, but similar issue - Ashni straight up died in my encounter and Johcris never shows up. Bioware forums are down now, if anyone knows a fix for this? Can Ashni be spawned?

The Bioware forums might be long gone, but fortunately KevL is stall alive and kicking at the Neverwinter Vault.
https://forum.neverwintervault.org/c/nwn2/6
That's probably the best place to ask.