Answer to OP is the most famous answer in poker. It depends. I have delayed a seat for a week because of work. It was early last year though.
Perhaps if you detail it enough you may be able to get it rescheduled, and don't forget the begging part. I have read where they may unregister you and give you the entry fee. I can see why they might not want to do this, but if you don't ask, they sure as hell wont.