Rosemary Dahl's mercenary team
Sebastien's last assignment came in 2503 when, under orders from a benefactor known as Mr. V, he and the rest of the team were assigned to safeguard a team of archeologists led by Jake Ramsey, excavating an alien temple on the world of Nemaka. The term "safeguarding" took on a different turn however after Ramsey was attacked by a protoss entity, orders being given to detain the archeologists until the arrival of the Gray Tiger. As it was however, the mercenaries were also taken into custody.
Death came for Sebastien on the ship, a rampant marine destroying its life support systems, leaving him to freeze to death and/or suffocate.