When his general was imprisoned on Kalaan after refusing an order to kill civilians, fellow stormtrooper Gana Lant convinced Rosan and eight other stormtroopers who had served under Tantor to put the man who had pulled them through battle-after-battle over the Galactic Empire that had turned on him.
In what turned out to be a catastrophic error, Grand General Malcor Brashin assigned them to guard Tantor in his outdoor cell. Lant freed Tantor and informed him of the squad's loyalty. With Tantor freed, the stormtroopers stole the TR-MB prototype and stormed the prison, freeing Luke Skywalker. The group trekked through Kalaan's canyons, picking up support from the Kalaanite resistance until they arrived at a Rebel base set up by Tyr Taskeen. From there, they were taken to Taskeen's fleet, where would presumably have been imprisoned temporarily along with their general. When released, they most likely continued serving the Rebellion as infantry under Tantor.