I seem to be having a problem towards the end of the blood curse questline. I have gotten the spear head from Vergen and come back and talked with King Henselt to start the excorcism ritual. We then go to Sabrina's altar where I guide him to draw out the diagram and then I light the powder to begin the phase with all the wraiths.
It is at this point that I seem to fall into a bug. I keep on fighting off the wraiths for what seems to be upwards of 10 minutes while Sabrina keeps on repeating her curse at King Henselt. My understanding is that King Henselt is supposed to stab her with the spear head at some point to end the ritual, but that doesn't seem to happen for me.

Has anybody encountered this before? If so, how can I fix it. I've tried going back to a few save points and still no good.

So has anybody else experienced this problem at all? Any suggestions would be greatly appreciated.

Not sure if I experienced this. But it might be dependent on how many wraiths you kill and not how long you fight them

I have not encountered this bug, but the quest makes it clear that it's going to take longer if Wraiths attack Henselt - are you sure they are not attacking him? Have you tried lowering the difficulty to see if that works for you? If you're really, really stuck you can upload your save file so others can take a look at it and help.

Yeah, the 3 wraiths all come after me. Henselt just seems to kneel in front of Sabrina the entire time as I roll away/fight the wraiths for what seems like forever. If I have this problem when I try again I'll post the save file

haven't encountered this, but 3 wraiths is not many, I think I kill 8 or 10 before he finally deals with her. Using red haze and axii to take control of one or more can make it less painful. The wraiths will respawn within 5 seconds of death. I think what you might be experiencing is the same bug that happens with the veyopatis quest in flotsam. if the wraiths attack the priestess there, she will turn around and watch a never ending fight. It could be that if the king is getting attacked, that it causes the same glitch.

Hmm, this might be related to how NPCs (in this case Henselt and Anezka) feel threatened by Geralt brandishing his sword and temporarily stopping whatever they are doing, meanwhile the monster spawning continues unhindered.

So maybe try sheathing your sword, maybe then the NPC will go ahead and do what they are supposed to do, and draw your sword again once they get to it?