Donations are non refundable. They have been used already to fund the game Battle Cry of Freedom, as evidenced by the weekly developer blog updates. You will still receive the benefits of donating, but should you find yourself banned from the forum, you will have been considered as giving up the priviledge to the donator board.
The gifts given as thanks for donations are just that, gifts. Should a user decide to violate policies of the forums in such a way as to be determined inconsolable and thus requiring a permanent ban, they have lost the gift of the donator board. They will, however, receive all other gifts of the level of donations met.