Shouldn't happen but if it does that is when booking through a good TA is essential. We had one cruise cancelled 3 weeks out from sailing. Well it did have a hole put in the ship's hull. The line was only going to refund what was paid but our TA got us an extra payment of $3000.
On a second occasion a river cruise had a totally different itinerary to what was sold. The company thought a simple apology was all that was needed despite the fact that the changes were a consequence of the captain running the boat onto a sandbank. We got $5000 back for that one.
On both times it was the tenacity and experience of our TA that got the results.
