If you quarantine him he will be there long enough to accept that as his new home. And he will want to be with the girls. He is not going to flee.
The question is where will they want to sleep? That could be where the girls sleep now. It could be near where he is quarantined or where the girls now sleep. You'll want to be out there at bedtime to see what happens regardless, but you may need to intervene. Or house him where the girls sleep in a crate for a couple of days to get him used to sleeping there before you turn him loose.
When you integrated them two things could happen. At that age he may mate one or two of them and then they are his flock. That can be about as peaceful and drama-free as any possible integration. Or your current dominant hen may be unwilling to give up her position as flock master. If that happens they will probably fight. It could be a quick fight or drawn out over a few days. As long as no one gets hurt no big deal. It's how they settle things. But check to see that no one is injured. You may need to lock one up, probably her.
With living animals you do not get guarantees. I think it is highly likely you will not have any problems. If I were in your situation I'd just let him loose and see what happens, you will probably be pleased. But with living animals you don't get guarantees.
Good luck!
