I think I would just caution you to try and set a firm end date sooner than later. There is a chance they will change their mind (a few times) if they just assume their space is there space until they decide to officially leave (they technically have already changed their mind once). So right now they plan to pull him in the fall...but maybe in a couple weeks they decide to keep him in until new baby is a couple months old. Then baby is born and they decide to pull him right away. I would caution filling their space for October now but waiting until 3 weeks before to tell them.