PennyHM, When I said you might want to rethink your plans, I didn't mean to change the dates. What I meant was it might be wiser to stay onsite Christmas week and offsite for your June trip. We too cannot go in the off season because of taking the kids out of school and end up going in June and the week after Christmas. We expect crowds and are prepared for it at Christmas. June is also crowded, especially toward the end of the month, but not nearly as bad as Christmas week. Sorry for not being a little clearer in what I was saying.
No, you will not be asked to leave once you are in the parks. If the parks close early, they will close it to outside guests that haven't already entered the park. They will still allow Disney resort guests in by bus or monorail. If it gets too full, they will not even allow resort guests, but I don't know if this has ever happened. If you leave the park in the middle of the day, you run the risk of not being able to return later because they have closed it to outside guests. If this happens, I've seen them redirect guests to other parks that are still open. Don't know if all the parks were closed at the same time.
If it were me, I would make sure I stayed onsite during Christmas week, but that is JMHO. If you decide to stay onsite for Christmas, I advise you to book the AS now as they fill up quickly for this time. I've had trouble booking AS for that time and have ended up at the moderates because they were already booked. Keep reading the DIS boards and check out Mousesavers.com and hope for discounts. If they have them, they probably will only go through 12/25 the latest if we're lucky. I'm planning on going also that time, so I need to call myself.