The loan term can run one to seven years. Long term loans may not be a good idea if you plan to trade the car in after three or four years; at that point you may still owe more on the loan than the car is worth.
If you do miss the ship, go into the cruise terminal and talk with the port agents, who are in contact with both shipboard and shoreside personnel. They can help you decide the best way to meet your ship, and start to pave the way for rejoining your cruise, which will be already in progress without you.
If you missed a day or part of a day cruise, there will likely be another cruise leaving a couple hours later or the next day. In this case, you may be able to simply wait for the next ship. Other cruise lines will offer a refund or a voucher for a later cruise, which can be some consolation for people.