Wingy, did you get a first hand experience in the past years about that? I'm not so sure it has all become as you say.
I dived the Andamans from Havelock ten years ago, it was wonderful as Dive India's karen guides had discovered the diving highlights of the area : Dixon pinnacle, Johnny's Gorge, Jackson's bar, etc. each named after one of DiveIndia's guide. You had to ride a longtail boat for an hour and dive into a pretty hard current sometimes, defintely not spots for the beginners.
They were quite deep spots 25-40m dived around a pinnacle or inside a canyon, often with such current that brought big schools of anything from anchovies chased by jacks to cudas, snappers, sweetlips, etc. Any fish that would school you name it could be seen on these sites, plus huge groupers, sometimes a manta.
I can understand it might has been somehow fished while the local operators tried to keep the bearings of these deep sites quite little known, the Andamans are not as populated as Thailand/Burma either.
The liveaboards would usually spread the word the place was not interesting because they dived the shallow spots of Minerva ledge for instance and were unable to find those deep pinnacles, except for Dixon's.which was soon dived by all the operators.
In 2010/11 there was a major bleaching event in the Indian Ocean that destroyed many shallow corals, Thailand likewise, though for the deeper current swept sites, I don't think it had a defiinitive if any impact.
Back in 2014 I read a report from a french diver who did his DM internship at DI and came back with the same site descriptions for the deep spots as I wrote above.
Hence I hardly believe a total destruction of the reef was achieved within the past three years... I guess we may not be speaking about those same "advanced" sites. Personally I have been thinking going back when I have time and money to : the best sites of this place were definitely not diveable for newbie divers..