Investors have so far seen the potential loss of more than a half a billion dollars in the collapse of a Lancaster-based ATM network. The total was revealed in new court documents that include a $455 million sales agreement from early November when network operator Daryl Heller was negotiating a total buyout of investors. Heller signed the agreement that indicated he believed the network’s assets to be worth that amount but he never came through with the money. The $445 million added to a $138 million judgment for missed payments from the network put investors’ total potential losses at about $593 million.