Or even if they have the electricity to be able to see at all.

It occurred to me that their final moments could truly be: trapped in an airtight tube, 3,800m below the surface, dwindling air supply, and no. light. Pitch darkness. No way to know if anyone is coming, how long you’ve been down there, or if the sub will instead (mercifully) give way to the pressure and crush you instantaneously and without warning.