My xah is currently sober and has been since January but has recently left his rehab supports so we'll see where that goes. He is back in the area as of last week.
I would like to be 'friendly' if he stays sober. I would not want to do things with just him, like I would with a friend, but I would like to be able to have a more friendly relationship. We can take the kids out for a celebratory supper for something. He can show up for their birthday party and it won't be so miserable. We can have phone conversations about plans. My concern with that is it would put me in a position to always protect my boundaries - always. He pushes for more.
If he doesn't stay sober he isn't nice and so I would want to keep it all business about the kids and keep everything separate.
ETA: Without the kids I don't think I'd want to remain friends with an ex but I would hope we could be in the same room together without freaking out (like if we had mutual friends etc.).