I'm 100% with all the thoughts appearing here, all the more gruesome in that we have to, figuratively speaking, sit here and watch it happen.
The oxygen hose through the hull's not really an option. Sub Hulls are spectacularly strong when intact. Start putting the required energy into creating a whole and you could cause a catastrophic failure.
They have escape systems on board, but one would guess that if they could use them, then they would have done so by now.
It might not have taken much to drag this thing to the bottom, and remember that the 'massive damage' reportedly in the nose/bow area could have been the result of of impact with the bottom.
On the manning question, the specialised nature of these vessels mean they are usually SNCO/Officer heavy, but I can't talk numbers.
I have no insight into what caused it, but I think I have a fair grasp of the enormity of the task of getting them out. To do that you need a hole. If you have a hole, then there's an entire ocean's worth of water wanting to go in.
Like the rest of you, I've got everything crossed for them.