There is no arguing against irrational fear, but cruising is VERY safe and Disney to date has never had to evacuate a ship.
In this very unlikely event however I must strongly advice against evacuating on your own. It will be your death if you even survive the impact of your dive into the water. A person alone without a beacon will not be found in the Ocean and die. Instead: go to your muster stations and get in your assigned life boat with 50 other people and trained staff. The lifeboat will last long enough for other ships to pick you up. Also it is clearly visible (big yellow floating) and therefor can easily be found by other ships or rescue helicopters. Think about the difference between picking up 40 visible lifeboats or 4000 hard to find individuals out of the Ocean.
Second: you will put other's life at risk as your lifeboat will not be launched until all assigned people have reported. If you evacuate on your own you will severely delay the launch of your assigned lifeboat.
Back to the original topic: chances are very, very small anything will happen on your cruise, but that is the same as chances are very small your plane will crash. Still many people are afraid of flying.