Outboard powered boats under 20 feet in length are required to have floatation to keep the level if swamped. My understanding is that there have only been one or two boats which were swamped (one from anchoring by the stern, one by getting into surf too close to the beach, due to engine failure. Both boats were salvaged.
With the floatation under the V berth platform and the balsa or foam core, the boats would not sink, but may not be level or may be capsized. The motor and batteries would drag the stern down, and the bow would be the only part floating above the surface. The good news is that these boats are very hard to capsize or sink even in rough conditions. Where the floatation has been removed, or there is no floatation, then the boat would most likely sink, unless there is enough air trapped under the forward deck. Having a windlass or deck pipe might let enough water in, that there would not be enough air to float upside down.
If you are going into extremely rough waters, then a life raft, or blowup inflatable boat is wise, just in case. Water will get into the cabin rapidly, both around the door, and thru the areas where cables pass thru to the aft part of the boat under the gunnel.