No, ADAT is not quite dead – it is totally dead. It is buried six feet under, tree roots are growing through the rotting casket, and no-one even bothers any more to read its name in the book of condolence.
If you still have a working ADAT in your studio, then frankly I'm amazed it's still working. Good luck to you – get every ounce of benefit from it while you can. Just make sure to copy your tapes to a medium you'll be able to play back in the future.
When ADAT was introduced, it seemed heaven-sent. Multitrack digital recording at that time cost the Earth, and ADAT machines came with a price tag that anyone who was really serious about recording could afford.
But ADATs were also dogged with problems. You could never trust an ADAT, that's for sure. There was always the possibility that it would do something 'funny' that you hadn't experienced before. It would have been foolhardy indeed to rely on an ADAT for live recording, without the backup of a secondary system.
ADAT recordings were also notoriously 'clicky'. Tiny little clicks seemed to appear at random and from nowhere like a sonic rash.
Individual ADAT machines could record eight tracks. The idea was that you could synchronize more ADATs to achieve 16-track, or 24-track (or more) operation. But they were so slow. Press play on your master machine and the others would race each other to see which could be the slowest to catch up. Mixing on ADAT was a slow process indeed.
Finally, the reliability of ADAT machines – terrible!
It was often said that if you needed 24 tracks of ADAT, you needed to buy four machines (4 x 8 = 32) to account for the one that would always be at the repairers.
OK, I'll admit that ADAT was a nice try, and it set a price benchmark that other systems had to match and beat. And the rival digital 8-track format, Tascam's DTRS, was spurred into rapid progress and became a very usable system. It is still in common use today in broadcast and post-production as a 'workhorse' bulk storage machine.
So RIP ADAT. Gone, forgotten, and thankfully never to return.
By the way, Alesis now make a hard disk 'ADAT' machine. Why they cling to that name, who knows, but it's a totally different animal and worth checking out.