Just got it late. Safari 17 is out now and skipped Big Sur. Sleep well, my friend.
Certainly not the end of the world 😂. Safari 16 will be relevant for a while and there are plenty of other competitive browsers. I'd say you have until 2028 with Safari 16.
It should be interesting to see the Apple Silicon adoption over the next few years. I don't see any numbers promoted anywhere (rather suspicious if it's so great) but if economic issues cause people to hold onto Intel systems longer this will extend the support lifecycle for browsers. And there's always Chromium Legacy.
The last consumer Intel machine was sold in 2020 making it practically new. The professional Mac Pro wasn't converted to AS until this year. So Intel still has legs.