Bbm,I would think that losing communication and therefore navigation would by protocol mean that the sub immediately heads to the surface.
I guess it’s possible they may be bobbing on the surface waiting for someone to find them. I think it more likely a catastrophic failure sadly happened.
That would be wonderful !
Although wouldn't they have some way to signal someone, like flares ?
Or have a tracking device on the sub that could be picked up once they're on the surface ?