I think you guys should start going around tomorrow and try to find a new big sponsor. If you can't get a big sponsor, try to get a few smaller ones. Do tons of fundraising (as much as you can stand. It may be tedious but it's worth keeping your team for). As others have said...if you're thinking about becoming a multi-school team then go to the other schools in your area. explain the problem. try to get funding from the school board. have a robot demonstration at one the schools and try to get kids involved. and if you become a multi-school team make sure you have good communication. I noticed someone said about having at least one teacher at eazch school. though this would make it a lot easier, it's not absolutely necessary. coming from a two-school team myself I can say this. We have one teacher and she is at the other school (not mine). we have a nice mailing list for the whole team. whenever there is news, our coach sends out the information via email to the whole team and we respond if necessary. It helps a lot with communication.
also to keep your team together in a multi-school team...try to have get-togethers. like parties. every year my team has a party at the beginning of the year and one at the end. these are just for fun and it keeps everyone friends. we have a few meetings a year. and our schools are basically rival schools. so we have friendly competitions when at the events as to who's school was announced. it's all in fun. but all in all, i wouldnt want my team any other way. it's perfect the way it is. so try to find more sponsors and do whatever it takes to keep your team alive. even if it means going to BEST robotics. it may not be FIRST, but it's still keeping alive your spirit about science and technology and gracious professionalism. I hope this helped.
