Large incision scab

My indoor cat (6yo male) had an accident a few weeks ago. Long story short, he got out and didn’t come back for a while, about half the day. He was acting weird so we went to the vet and after x rays and ultrasound, they discovered major inflammation and a potential foreign body. They cut him open to find a stick about 6in long had impaled him and broken off to where the whole thing was completely inside him. It was impossible to see the entry wound before they shaved him because it was rather small, like the size of a chopstick. Anyways, the incision was quite large and at this point in healing he had a big scab. He had an antibiotic injection post op and another one when he got his stitches removed. I took him back a few days later because his incision had opened in two places, but they were more concerned about his huge scab and infection. He’s now on a 5 day course of pill antibiotics (a struggle) and I was told there’s a decent chance the scab will fall off too soon and need to reoperate. My question is, is that a normal healing process? Do cat scabs fall off too soon? How likely is it really that he’ll need another operation? Thanks!! scab pic