The paragraph literally starts with "if"...

Which is why I used the caveat “if a significant percentage of users” do this. If not then fine, but if they do, I don’t think it’s an exaggeration to say that we can all say goodbye to Facebook. That’s how big of a problem this would cause.

They apparently announced that they’re getting into online dating today. Maybe the plan is to knowingly decimate the ad platform and charge for dating at some point. They’ll have massive layoffs and have to sell datacenters, but could at least keep the lights on for a few remaining employees managing the dating service.