He puts it this way: "Disney will be completely retooling FanLib with a focus on its own properties, instead of fan fiction and other networks’ TV shows and movies."
Ali does not seem to be aware that FanLib had two segments: the fanfic archive, and the crowdwriting software used for corporate marketing campaigns.
As soon as the Disney buyout rumor appeared in early June, FanLib members speculated in the forum that Disney would close the multi-fandom fanfic archive and focus on Disney's intellectual properties. It is a pretty obvious move, if the Disney buyout rumor is true.
Pirates of the Caribbean, a Disney property, was one of the largest fandoms at FanLib, based on the number of stories posted.
Rafat Ali has been the only source of the Disney rumor since the beginning -- every news article links back to him. As recently as a week ago, he reported the Disney deal might be off, so whoever is feeding him information can't be too close to the action.
The Mimbo brothers (Chris and David Williams) remain silent on the reason for FanLib's closure.
Disney has been buying up social networking websites (Club Penguin may be the largest) for years, and has rarely commented on its purchases. However, if the rumor is accurate, we can expect to see a Disney crowdwriting offering in the future. Since Disney already has a huge online presence, it could incorporate crowdwriting into an existing site.
Edit: Another reasonable hypothesis for FanLib's closure from alicornmoon, dated July 25th: Disney was set to buy FanLib, but the deal fell through, prompting FanLib's venture capital backers to pull the plug.