Here are a couple examples of disappearances:
The team from Plymouth Mass (124?) used to host a big off season event called the Rumble at the Rock. I believe they tried
very hard for a Chairman's award, didn't win for a couple years running and then pulled up stakes and joined the battle bots.
(This team is my reason why I get a little nervous when we discuss what we should do to do better in the Chairman's award race. I think they got burned out

. I would prefer to stay in FIRST than to stress out over awards)
Closer to home. The team from Windsor CT did well their rookie year, disbanded after a difficult second year, and then joined the other team from Windsor CT: 571, Paragon. The combined team is a very strong team now
Some private schools in the area have had teams and then disbanded. The Kilowatts and I believe a team from Mrs Porter's school

Those teams were small like the original 571, and perhaps if they had found a neighboring public school to team with they could have kept up the program.
FIRST is a tough program to maintain at a small school. We added Suffield to Windsor Locks in 1998 and it has helped a lot. Its nice to have enough students to have a drive team, pit team, scout team and spirit team without every student having to do everything.