They're most likely gonna be fine, it's a cliffhanger at the end of a chapter, I think Fuji will pull something off.
Asa/Yoru are a Fiend, so drinking blood is a good idea.
Maybe Denji can hurt himself and regen Asa/Yoru like she did for him during the Falling Devil arc?
That would be a nice parallel, seeing as the past few chapters have a lot of parallels to the Falling Devil arc.
If Yoru's part of the brain was hit, then whatever.
If Asa's part of the brain was hit, then I'm gonna kms.
I doubt either will die, desu, both are gonna make it out.