After exmatriculation you can use your student account up to the end of the next following semester. That is to say, if you exmatriculate on 13 December 2011, your authorisation for using your account is valid up to 30 September 2012.

Presumably your e-mail address remains forever. You can also undo a set e-mail forwarding to another e-mail address if you would not like to receive mails from your university account anymore.

exmatriculation account