While he's taken the field on occasion(what, once?), Sun-Tzu seems like the kind of guy to leave the fighting to the people who are actually good at it. While he might maintain his mechwarrior training just in case, I doubt he'd actually participate in something as risky as a combat drop. Might be his 'mech though, they did send it out during the worst fighting on Sian with another pilot, and it did a wonderful job of drawing fire.