Zelos will not be happy to see his not-boyfriend-honest killed. At all. Of course he'll want to help, even if it's just trying to sneak in and grab Sakura behind Gilgamesh's back, but he's likely to run away if it looks like he'll have to confront him directly.

Midboss, meanwhile, will be focusing on trying to get Attleton back with every force he can. He still hasn't learnt since charging Lucifer head-on, so will probably be taking this approach with Gilgamesh. I'd rather he not get killed (since that literally happened last event), but I'm all for him getting seriously hurt.

Izanami will mostly sit back and observe. She has no reason to get involved despite argubly being my most powerful muse if Midboss' canon didn't have such rediculous power levels.