Same as 5LM. If they want their spot they need to pay full-time for it. There is never a guarantee either that I will have room for baby.
I have had 2 great families that have come back after leaving. I always kept in touch and the minute a spot opened up the grabbed it and came back. In the meantime they got to experience what a different provider was like and I find they appreciate me so much more now. I have one mom on mat leave now on my waiting list for the baby next fall.