[Tottanka]

First of all, you ahould try talking to that group of people who left. If that does not work, I'm not sure there is anything you can do. It could be nice if your team held it and found sponsership and all it needs. I'm sure you guys can still be FIRSTers, but if those 2 teams become enemy-like it will not be GP at all, and therefore not with the spirit of FIRST. You should see how it works.
Are those 2 teams gonna be from the same school, or city?
Do you want ti recruit the same members?
If those 2 question have a positive answer than you have a serious problem, and mabe even should contact FIRST.
Hope i helped, Liron.