[Eugenia Gabrielov]

It sounds like this is an issue that is really bothering you. Here are a couple things you might try:

Ignore the diversity issue for just a moment, and look at the students that dropped out and came back on the team as people. Did they drop out because their work was hard? Did they drop out due to family issues? Maybe some of them didn't, but give them the benefit of the doubt and see where this season takes you.

If other students feel the same way, you might try to have a private meeting with the team leader to air your concerns, and to outline a plan for how to handle the situation in the future. If you would like to make it impossible to come back after dropping out (your team's judgment), write that into the constitution (if you have one). Make it clear that members who drop out can't come back, otherwise you're out of luck I think.

Finally, please take this to heart: this is clearly a sensitive issue. What we provide here are guidelines, possibilities from our own experiences that may help set you in the right direction. This call is yours' to make as a team, as a group of people with a common goal, not just as a bunch of people of different races and genders.