Defunct brands-

Verity

Altis Audio

Merlin Musical Systems(just had my driver's upgraded by Rich Brkich)

Audio Magic 

Counterpoint 

Jerry Ozment's tube dac(can't remember the name). 

It's easier to think of what IS still around from the high end as it was defined in the 70s and 80s, rather than what brands are defunct.  Nearly all of the best are either gone or someone bought the name and now sells much lesser gear under the same imprimatur. McIntosh, which actually dates back to the 50s, is one of the rare exceptions. I guess Conrad Johnson is old enough to qualify as an exception.

The 70s and '80s are respectively 50 and 40 years ago. It takes a lot for business to last that long, especially in a volatile and Niche industry.

I remember back in the early oughts listing after Halcro gear sound unheard simply because the way they looked. They're still around, though I think they've bounced around ownership over the years as well as visibility.