Return of Reckoning

I did the quest like normal. Everything works well until fighting the boss as a tank. I fought it until someinternal mob timer despawned the enemy, this took quite long maybe 5 to 10 minutes. As I was unable to kill the mob and didn't die myself, it left the qquest stage uncompleted, and it left me unable to try fighting the boss again. Tried getting a new Wailing Horror to sacrifice to do it again, but it wouldn't drop the item anymore. Then I tried abandoning the quest to retake it, but the quest doesn't appear on the npc. I could track the original Frostvein Fury to get a new Nachtblum's Bookbag, but it does nothing. So now the quest cannot be regained either.

1. Do the questline until the final boss like expected.
2. Survive the final encounter without dying or being able to kill the monster in time.
3. You cannot attempt to fight the boss again or get the quest again if you abandon it.

I waited a day to see if I might be able to do it the next day, but the issue remains :S
It's not a big deal if I have to be without it, but I figured I'd write about it and posted an issue.
Any ideas what more to try?

interact with quest object again (what require boss spawn)

Didn't work at the time, and now the quest is abandoned :S

didn't work for me either but I hope this will work fine after some point