In the case of Princess, they refunded the cost of the cruise and airfare. They wouldn't refund the cost of the pre-cruise hotel. They said we will get 25% off on a future cruise.
During the last day on board, things normally charged to your shipboard account were free. I made several phone calls from the ship and used the Internet Cafe to cancel some tours I had arranged. Unfortunately the shops and casino were closed, although some people got free spa treatments and purchased things from the spa before they cancelled the cruise, so that was free.