If they are a good fit and you have room, why wouldn't you take them back? If you are full, then you're full. Our gym has taken girls back after they tried another gym and it wasn't the right fit.
It happened to my 7 year old last fall (right before her first meet!). She was able to do ROBHS x 3 and suddenly couldn't do one. I took the wise advice of many here and never talked about it. The coaches did not made a big deal about it and she was soon back to flipping.
We used to be at a Y and had practice all summer.
OP- have you looked at other gyms? My 7 & 9 year olds will be going 16 hours over the summer. I can't imagine taking the summer off.