You don't need to untie it when you get off the boat. The bill will be delivered to your cabin before disembarking. If you have any questions, please inquire at the front desk in time. If the bill is all right, get off the boat and leave without any formalities. You don't need to return the room card. You can keep it as a souvenir.

I wonder if all cruise ships are like this? At least that's what I always do.

As for whether it will be stolen, I think the probability should be extremely small. After all, there are thousands of people taking cruise ships every day in the world, and everyone is like this, so it should be safe.