1) High end audio has always been a niche market. I've been buying high end gear for 45 years and I've rarely found any of my friends or acquaintences who were into the hobby like I was. Also, there is no similarity between Apple earbuds and the enthusiast audio market. Apple is a mass market company. Denon and Marantz are the proverbial fly on the elephant's butt.
2) High end audio has been dying ever since I entered the hobby. Oh, wait, it's bigger than it has ever been....
3) New companies have been entering the market and established companies are expanding their product lines. This is not indicative of a dying industry. Look at the Music Direct catalog and tell me that the industry is shrinking and dying.
4) The ultra high end is exploding. We may sneer at speakers and amplifiers that cost $100K but someone is buying this stuff.
5) The value end of the industry is solid and growing. Schiit, Topping, and SVS are excellent examples of companies that are selling tons of very high quality gear at reasonable prices.
6) The chances of Denon and Marantz disappearing are zero. These companies have the most recognizable brands in the industry, they are selling hundreds of millions of dollars of gear, and they have a strong dealer network. Masimo will sell their audio division for much less than they paid for it but it will survive and prosper.
7) I'm running high end gear from the 90's (Krell and Thiel) and I've been to 3 audio shows. My observation is that the state of the art has not improved much from 30 years ago. I've listend to many systems where the cables cost more than my entire rig and the sound did not equal my setup.
8) This is the golden age of audio. There are lots of very high quality components available for reasonable prices, you can stream millions of titles of high resolution music for an absurdly low monthly price, and there has never been more used luxury gear available. But nevermind, the sky is falling.