30 years ago they would have absolutely heard it and triangulated it's position within minutes.I also have been watching this since the beginning and I thought more toward hypoxia than implosion. The first indication of a problem was when communication was lost, though nobody could find any reason for it. I think they just quietly fell asleep and there was nobody to play with the game controller. If, in an uncontrolled descent, it could be miles away from it's intended track.
I doubt that the military would admit to it, but I'm pretty sure an implosion of that size could be heard by military underwater listening devices from hundreds of miles away, if not more.
And the Titanic claims 5 more lives 113 years after the original disaster.
There is not the same threat now and I am not sure our undersea listening program is as robust as it once was.