I'd be really surprised if Dropbox didn't have a way to revert this (and to punish the Dropbox for Teams account creator, if identifiable).
What should've happened is this: revoke my access to the team folder and downgrade my account back to Free. (Then, annoy me and refuse to sync until I go down to 2GB of usage.) That would be good design.
That in itself is okay, but then the conversion mail should have come with big, red warning notices; not the bland email you seem to have received.
Ann has an individual account. She joins a team. She leaves the team, and Bob (the team account owner) revokes her access. Dropbox deletes all her accounts.
What can dropbox do here; set Ann back as a member of that team? Bob (paying a lot of money) is not happy with that.