"When" they do that, it will be because they have judged that they have, by then, thoroughly extinguished all competition. If you (the royal "you") want there to exist an alternative browser to which to jump to when the time comes, then consider making the jump today, when your influence might still make some small contribution to the competitiveness of the browser market.
Chrome serves me just fine nowadays. Unlike you, I'm not some kind of Gandhi of the tech scene or anything like that. If it serves me fine I won't stop using it. If Chrome ceases to support adblock extensions then I will go look for some other browser, I would probably change to Vivaldi or anything like that, or even Firefox, they sure as hell will be there.
