From the experience in 'Sharm' after the flight ban, I would imagine the reefs will start to recover quite quickly, both the physical reefs, and the related life that make the reefs their home.
For those of you luck to live in these places I think the diving will progressively improved (assuming they are still allowing you to dive). If you feel that it is anti-social to continue diving, due to the (low risk) of needing medical or rescue services during this, time. I would imagine snorkelling is probably ok.
Ultimately, all those of us who use the sea, professionally or for recreation, will benefit.
The mix of fewer divers, boats, etc will, (rather like the cities,) reduce pollution and the adverse effects of human foot (fin) fall.