If you cancel your payments, your data will not be deleted: the data is hosted free of charge until you start a new plan.
If you erase your account however, all of your data will be deleted and you will not be able to retrieve it again. You would be deleting, for example, your subscribers, campaigns and all click and open statistics. Much of that data can be exported, and a copy of your database is available on request.
You can cancel the recurring payments on your account on the Payments tab of your account page. To do so, go to: