If I were Dropbox, and designing this feature, I'd have created two folders inside the master Dropbox folder. "Personal" and "Teams" then inside the "Teams" folder, I'd have created a folder for each team a person is invited to join. I realize that structure wasn't in-place when Dropbox was first created, complicating the matter - but it seems like it would have provided the cleanest way to delineate what files and access would be revoked when a user is removed from a team.