Many years ago I witnessed a Buccaneer do a vertical dive into the Johore Strait following loss of control and the crew ejecting. All I saw was a huge fountain of water from each wing. It was later recovered basically intact having slowed very rapidly and settled on the bottom in shallow water. If a 777 did the same it would likely do serious damage to the front end and the wings/engines would break off but the cabin may remain more or less intact and the whole lot would sink to the bottom, any air having been expelled through the damaged areas.