Sometimes, there are companies that are still around but are a shadow of what they used to be. Seems to me Adcom fits that mold- they used to be a much bigger deal.
But as for gone and lamented- let’s add Dahlquist, Dynaco, Hafler, Counterpoint.
And I’m still feeling burned that Auralic is gone- no more firmware updates and I know one day my Auralic streamer will be bricked. On the other hand, I’m confident that long after I’m gone someone else will be enjoying the hell out of my Thorens TD124. With a caring owner, it will still be making music when it’s 100 years old