The players seem to be reeling a little from the beginning of this combat. The soulknives definitely have them worried, as well they should be. The biggest problem I see right now is that they might be starting to forget some of their capabilities. In this situation, Morrus seems to be counting on them to be on top of their game. It's possible that one or two poor decisions could swing this in a bad way.
Morrus, it looks like you have done a great job so far and it sounds like everyone is having fun. Even if the players aren't so sure they will pull through, they seem to be enjoying the challenge. In al likelihood they will get over the doom and gloom through the week and start coming up with plans to pull this thing out in their favor. But they might also get stuck in a bad rut with their thought processes. It's something to keep in mind.
I believe the cleric said he had a feat that lets him use a turning to swap out a prepared spell for something on a domain list? And he has the Healing domain? If so, the PCs should be able to address the ability damage. Well, so long as the cleric's Wisdom doesn't drop too low to cast anything. The PCs aren't done for by any stretch of the imagination. But they could blow it if they get panicky.