Chrome has 65% market share (according to Statcounter), far from a near monopoly. Even if you add Edge (which you shouldn’t because Microsoft could fork Blink at any time), you only get 70% for their web engine. Around 2003 or 2004, IE had like 95% market share (and many websites required Flash Player) and we now know that that was eventually defeated.
I am all for worrying about the decline of good things, but your scenario isn’t something I’m worrying that much about.