I was also surprised by this news.
It does not actually seem to be shutting down, just one very drastic change.
I can understand getting tired of the day to day bits of running the site, but it perhaps might have been better to get some volunteers to run the site for him.
Sort of keep it all under the same site, but instead of breaking things up, let the people who are are taking various pieces and spinning off to start their own web site, instead just manage that section of OG.