Maybe all of you strong people who have left have it all figured out, but unfortunately for me, I don't have that figured out yet. I don't trust the system AT ALL.
Can you trust in your HP?
I am fortunate that my A is no longer functional enough to make a stink about custody. Also we were never married, so he would technically have to establish paternity first. (And I took all that paperwork with me when I left, so he would have to go out of his way to do it). I literally just took our son and left the state. Despite all his (and his mother's) quacking about their "rights", I have yet to see any evidence that they are willing to take on even a minimal visitation. I try make sure they speak to DS4 every week, and A can't even manage that some weeks. He forgets what day it is, can't dial a phone, is in the drunk tank, whatever.
I offered to let him (with his parent's supervision) have DS4 for a week at Christmas b/c DS12 is spending the holiday with his deceased father's family. We're meeting halfway to do the exchange, so I told A that he was welcome to have a weeklong visit if they wanted to meet us at the halfway point- which for them is only like a 3 hr drive. The reply so far- crickets. Alcoholics say a lot of things, but what they do is drink. Supervising children, cooking for them, paying attention to them, those things all require effort. And when an A gets to a certain point, all of their effort goes into drinking, anything that interferes with that will fall by the wayside. Your AH may not quite be at this point yet, but he will be one day, whether you try to keep the family together or not.
It's easy for him to come home and do whatever he wants because someone else is there taking care of everything. When I left, mine was dismayed that he suddenly had to do his own laundry. That was his main complaint. A's are not big on extra responsibility, and kids are a big responsibility when you have them all to yourself. Another poster hit it on the head when she said that he would likely start coming up with excuses not to do his visits after a few weeks of the "superdad" act.