The survival of Bitcoin-trading exchange Mt.Gox was in doubt Monday after its CEO left the digital currency’s top advocacy group and the exchange’s website went offline. Mt.Gox chief executive Mark Karpeles resigned from the Bitcoin Foundation’s board of directors on Sunday. The exchange’s website then went down late on Monday, and visitors to the site saw only a blank white page. Users reported via Twitter that Mt. Gox was not executing new orders, raising the possibility that the exchange was also offline.