Ok I'm playing new game plus with the very latest updates installed. Decided to take on the "Missing Son: qiest and headed out to the castle to find the son after searching around finding a couple of bodies; dead of course. I come across a named fiend. His/Her name is Morvudd and we start fighting one another

Now I can take him all the way down to nothing at the castle.but he don't die even thugh his life bar is empty.

Isn't he suppose to flee to another area where you actually kill him? He don't die or flee any where.

Wonder if when they upgraded if they might have broke this quest . Does anyone know?

Any help would be appreciated. Thanks.

Invulnerable characters are almost always down to a corrupt installation and/or mods. Remove any and ALL mods, and verify/repair your installation.

Yes, he suppose to flee, then you need to track him and kill him in a second battle.