M.D.
We used my sitter for no-school days once the older two were in school. The youngest was still with her, but we'd still contniue doing it if she had room. She has filled their spots and I completely understand that. No sense in saving spots for a few days a year.
But I think it would be good for him to go back to a place where he is comfortable and has fun. The other option is to find a babysitter that can come in on those days - for a more reasonable price maybe. My girls are happy with $50 per day, and I'm happy to pay it. I have awesome babysitters too. Now I know that rate is low for a day, but I also give them both plenty of paid time off - so it evens out in the end and we both know this :).