Technically, without an agreement, she has rights to your son and you do too. She could take him to another state, but you could too.
My fear is once she takes him out of state, she will not be agreeable to having him come back. Once the child leaves the state, a precedence is being set for his care. I don’t know what the interstate jurisdiction is for you going up there and bringing him back.
I don’t know…tough situation to have to deal with. You are going to have to have something legal drawn up. If you leave it ‘open’ then you’re taking a risk, in my opinion. Michigan is a long way to travel.
IN MY OPINION, it would be best to have your parents keep him (in NC) while you and your wife deal with the issue. That way he has access to BOTH parents…which is the best.