I know a few people that have declined their offer of admission in Early Action and November round to go to schools such as Kellogg, for example, but have not done so until March. There will definately be some spots opening, but there is no way to know how many, or how many offers were made, or how many people will be admitted in the April round, or how many will pay and then go to some other school.
That's the beauty of being waitlisted! You never know!
Or are you going to tell me that you would trade this wonderfull feeling of not knowing if you are going to be in business school or working by this time next year for the joy of already be planning your pre-school vacation?
All jokes aside, I've declined my spot at Ross (with $$). So, from now on, it's either Tuck or nothing at all! Kinda scary, now that I think about it...