Perhaps I slept through "Cruise 101" but I thought this would be covered under the cancellation clause of your travel insurance? However, I went back and looked at my travel insurance policy we purchased for our last cruise and it did not cover being bumped. Which is something I was unaware of. I think that on our next cruise I will look at this a little more closely and see if there are policies that offer this sort of coverage.
Cruise bumping is basically when the cruise line cancels your cruise, usually to charter it to a private party. Do you remember the big stink that was produced when NCL cancelled several peoples long awaited cruise on the Pearl to charter it to Rosie O'Donnell and friends last year?
We can be more flexible than most folks with regard to rescheduling. However, many people get only one or two weeks of vacation a year and rescheduling is not an option for them, those are the people I really hate to see this sort of thing happen to. There ought to be a law, lol!
With regard to the original poster's question, how one should prepare for bumping?
I guess I would just simply be prepared to raise lot's of hell until they see things my way, or compensate me to a degree I am not angry and frustrated, or losing additional money due to them bumping me anymore.