Hi there. I’m sorry it took us a while to respond…I’ve been pondering over this since you initially posted. I think you may have to consider permanent separation. This is doable in a cat household, as you’ve seen, though it can be annoying, but it might be safest for the clowder.
I assume you’ve tried Feliway?
Soft tissue can take a LONG time to fully heal, and I think the “when” questions are best addressed with your vet who knows him best. In the interim, though, I’d start working on brain games! There are things you can do at home with him leashed which will work his brain and pull him out of his depression. My favorite is nosework – Fenzi Dog Sports Academy has a class you can do at home. I STRONGLY recommend it. Here’s the direct link: https://www.fenzidogsportsacademy.com/10-course-descriptions/13342-n101s-nw101-introduction-to-nosework