Nope, you can only make sure they do not get new data. From https://www.dropbox.com/account#manage https://www.dropbox.com/account#manage (pressing "unlink"):

Nope, you can only make sure they do not get new data. From https://www.dropbox.com/account#manage https://www.dropbox.com/account#manage (pressing "unlink"): "[The unlinked] computer will no longer stay in sync, but it will keep a copy of any file it currently has."