As long there are investors willing to take Ripple from his hand and there is a demand for Ripple, it won't impact Ripple prices. It was not uncommon for founder or chairman to selling their stake in stocks of their company. Though to make sure that action not sending the wrong signal toward investors, they could secure a deal with someone to overtake their bag. From what I saw, Jed McCaleb didn't do this so I think Ripple prices only be impacted if he dump a lot in one goes.