Related, but concerns boarding at a midpoint rather than ditching: Can you take only part of a cruise?
After reading the above question, I was curious about the opposite scenario. My passport allows me indefinite access and automatic residency on several Caribbean islands that are frequent cruise ship ports of call. If I take a cruise that stops on one of those islands part-way and decide that I'm going to stay there, the government isn't going to be on my case as long as I do my homework (e.g. checking in to obtain local ID if I decide to live there, or else staying out of trouble and flying home eventually if I decide to just hang around as a tourist for a while). What happens with the cruise?
Generally, what happens if you ditch a cruise part-way? For example, are early departure fees (getting billed extra for not getting back on) typical, or is blacklisting (being banned from cruising again on the same ship or line) common? Do they simply not care and clean out your cabin?
I'm especially interested in the Caribbean but answers can address other regions of the world (e.g. Europe or Asia) if you have knowledge of them or if practices differ from those typical in the Caribbean.