If you're thinking along these lines, you'll enjoy reading this post[1] by Venkatesh Rao. Stephen Fry leaving is the exact scenario of "evaporative cooling" expressed there, and you are exactly describing the process of "warrenization" that is required for large-scale online communities to survive and thrive. Obviously Twitter has failed in including these insights into their social architecture, to their detriment[2].

[1] http://www.ribbonfarm.com/2010/12/07/socratic-fishing-in-lak... [2] http://techcrunch.com/2016/02/10/trying-to-fly-with-broken-w...