Halls of torment

blmetels

Does this quest not have any checkpoints? And i thought tharn isnt supposed to run off and attack you if your out of his reach...i am using a bow. Is this bugged after 1st attempt?

Nephimana

The main quest doesn't save progress mid instance, if you disconnect, log out or leave mid quest, you have to do the whole thing all over again. Theres nothing you can do to retrieve it, you just have to do it again.
As for the tharn, most bosses have mechanics that don't encourage being far away. It's probably his mechanic, just check the kill feed if you die and see what it is. If it doesn't look right, report it.