I've read a few articles on this and have more questions than answers.
Initial reports seemed to suggest that it either imploded or got trapped. Either would imply that it was at the bottom. However, I read somewhere that they lost contact when it should have been about 1/2 way down. That almost certainly means it didn't implode and there wouldn't be anything to get trapped by.
There have been reports of pounding at half hour increments which means those on board are alive (assuming the noise is coming from them) but it is obviously unclear what caused the issues and finding something that small 2.5mi below the surface is a tall order to say the least.
I've read that they should have enough oxygen to stay alive until sometime Thursday so at this point it is still a search and rescue mission but if they are not retrieved within about 24 hours it will be downgraded to a search for bodies and other evidence.