As he's ill I would just let him eat what he wants. It's better than him not eating at all! Cheech stopped eating her pellets so I've given her muesli. Not great I know but if it means she's eating.
Critical care is a powder you make up with water. Some will eat it off a spoon or from a bowl but you often have to syringe feed. It really gets stuck in the syringes though! I've been soaking pellets and using a blender and syringe feeding that. Critical care has lots of stuff they need if they're not eating properly.
I can tell you're worrying yourself sick. It's happened and you're doing all you can, you obviously care a lot so just keep it up. Ask any questions you want, I've just had this happen to me so if you need any help or advice just message me. I am in England though, so some stuff might be different, but I'll help all I can. Good luck to both of you!