Some engineering care has already gone into not just completely abandoning the cargo compartment if the plane needs to do an unpaved-land or water landing! Yes, the passengers' lives are more important, but dath ilan doesn't feel the need to show how virtuous they are when it comes to not caring about mere possessions. Sometimes people put things they care about in their luggage.
If the plane made a water landing, it would not, of course, sink. In many plausible scenarios, like "suddenly needing to land into rough waters in the middle of the ocean after losing all comms somehow but not suffering engine damage", you would want to keep everyone on the plane for a while rather than entrusting them to inflatable boats. So the plane can float indefinitely, if you cut loose the engines and some of the wings; not literally through hurricanes, but in fairly rough waters.
It'd be possible to access the cargo compartment from the cabin, once water-landed, via opening an emergency hatch. Keeping the cargo compartment watertight is part of how the plane stays afloat.