Agreed that if you flood a digital camera it is a paperweight. However many leaks don't result in an out and out flood. With a Nikonos it was always a debate if you should rinse the camera in fresh water. I would not do that with a digital camera. I would use a damp cloth to wipe it down well.
A small hairblower is of value. You can convert a cardboard box to a tent and use the hairblower to dry off the camera thoroughly. A small bottle of electronic contact cleaner and some q tips can be of value if you have corroded electric contacts. If you housing has a hot shoe and you can get an extra hot shoe and/or an extra strobe synch cord socket you might keep shooting.
Get the battery and the memory card out of the camera as soon as possible. Beware that if you flood a synch cord there may be salt water in the cord even if you dry it thoroughly. If you try to use it again you may fry the electronics is your camera and or strobe.
As always bring your duct tape, some thick rubber bands, and some zip ties.
Best thing is to always test your housing in the rinse tank anytime you open the housing. This way you are mostly likely to have a leak and not a flood. You will then have a reasonable chance that the above may be of some value.
If you are using a dSLR decide ahead of time if the lens or the camera is of more value to you. That way you will know which way to hold the house if you detect a leak at depth.
You best choice would be as mentioned by others to have an adequate back up. Your camera/housing/strobe may not work on a trip for other reasons than just a flood. Fortunately digital cameras become obsolete so fast that saving your old rig as a backup may be a better choice than trying to sell it at a loss.
