I'd bet the engine is locked up. If you were driving through the water, you hydralocked the engine. Water does not compress. If water was in the pan, the only way it gets there is through the cylinders. I've seen these engines hyradlocked before and I'd almost bet money that one or two connecting rods are bent 90 degrees against the block. This type of damage doesn't necessarily punch a hole in the block. Drop the pan again and look up into the block. Look at the connecting rods and see which rods are wedged against the block.

If you have comprehensive coverage on your insurance, it's covered (your insurance coverage does cover stupidity). Depending on the van's mileage, I'd bet the insurance company installs a used engine or totals it.