“No comment” sometimes means more than “no comment.”
Sony has trotted out the usual line about now commenting on rumors and speculation, but if Ueda was still working at Sony, it’s strange that Sony wouldn’t want to stamp out this rumor right away.
The Last Guardian has been delayed several times, and is tentatively slated for a 2012 release. If this report is true, it's unclear how or if it would impact the game's development.
The developer has not disappeared from the Internet, however, and updated his Twitter account as recently as a few hours ago. He has not commented on the reports regarding his status at Sony.