Went to Vooriden.
Got quest from Edwin Wallows.
Got Murgo.
Went to Torin Quarry, fought baddies along the way.
Got large stone, gave to Murgo to carry.
Went back to Vooriden, fought baddies along the way.
Upon arrival at Vooriden, Murgo is gone with the stone.
Murgo not anywhere in Vooriden.
Edwin Wallows's dialoge options indicate quest is still not done, same with quest log.
Large stone not at Torin Quarry.
Don't have old save.
So Murgo is MIA with Large Stone. He was in my party, unhurt, with no other items, prior to travel to Vooriden.
What do I do? Is the reward just money/exp? Or is this an important quest? I fear it is, due to having to pray/get blessings from the old gods, I think, and this is one of the old gods altars.

The quest is meaningless unless you want to get a blessing from Halcyon. It's also required if you're after the ultimate blessing.
If you don't care about Halcyon's blessing or the ultimate blessing, feel free to move on. The XP gained from the quest is easily made up for with a couple random encounters.

Thanks - that's the info I needed, but that also confirms my fear (ie it's not a stand-alone quest). Is there a known character modifier program for this game? I just want to add the stone to one of my other non-dissapearing NPCs. I don't want to cheat in this game, but I don't mind if it's fixing a bug.

I haven't used and so can't guarantee if this program will help, but try this thread over at Terra-Arcanum:
[url=]http://terra-arcanum.com/phpBB/viewtopic.php?t=15917[/url]
If that doesn't help, try digging through their forums.

I use Virgil's Debug mod all the time I find it to be rather invaluable in creating the ultimate custom characters.

Agreed. I've had to restart, but the Debug MOD has been a timesaver for getting me back to where I was.