I don't see how that follows in several ways. First off "waste" is deeply subjective in many ways - wasted by whose standards? Is time spent at work wasted or time not spent at work? LPuritans had ideas of "wastes time" which were so unpopular they had a return to monarchy they ousted. What would "coming to their senses" entail?

Even then how would it create a global economic collapse? I doubt even a complete advertising melt-down (probably impossible situation where effectiveness of ads goes to 0% and it is known) would accomplish more than a recession or depression at most as even uninfluenced people would have needs and desires to meet and global trade could help fulfill them.

Even if a productivity glut drives down the value of labor that would self limit with minimum wage and "working more would get me less of value than taking more time offc

I'm not convinced the global economy is that bound to social media use. Why do you say?

And I’d bet if that did happen, which I think is extremely unlikely, the global economy would benefit greatly by people finding new uses for their time (not all of which would be productive), as opposed to funneling data and ad money towards Facebook.