He's revived humans before, easily. The Little Queen, who's energy he took, was bringing an entire planet back to life. Lambda and his....former host started outright creating the nova monsters after a while, instead of infecting existing ones.

I don't think he could...revive Tu Vishan entirely, because he'd be dead with it, too. But...I'm hoping he won't have to, sir.

[They just need time. That's all Asbel's been hoping for. Not a cure, not a permanent fix, but time.]