Sonak and a female crewmember were killed in a transporter accident shortly before the starship left to deal with the V'ger crisis in the mid-2270s. The ship's transporter was 'temporarily' out of order that time; Janice Rand operated the transporter when she saw their silhouettes being deformed, and despite Kirk's attempts to complete the transfer, they disappeared. When Kirk asked Starfleet if they ended up with their disfigured masses, a transporter operator at Starfleet Headquarters said what they received mercifully didn't live long. Kirk instructed him to contact Sonak's family through the Vulcan embassy to extend his sympathies. (Star Trek: The Motion Picture)