Yeah, believe me, I wanted to get rid of Sun-Tzu, but he is too smart to try something at this moment that justifies him getting shot. He didn't raise a weapon, he didn't leap to his mother's or sister's aid, and other than trying to (pro forma) claim the throne in his own right, he is cooperating. I wrote it out four times, and had him in die in three of them, but they all seemed forced and contrived. Really, this was the best way I saw to write it.
Death Commandos betraying the Chancellor? 
What Trace said.

Of course, you could also be talking about Loren Jaffray (Sub-Commander Jaffray), but he didn't actively betray the Chancellor either--and he has a history in BattleTech of changing sides anyway. In canon, Candance and Master Rush were engaged in talks about the future of Romano's rule--Master Rush even killed both her and Tsen in canon in 3052, just a year from now. Remember that Ion Rush is not a Death Commando, he is the Master of House Imarra. Candace counted on (gambled, really) that Rush's dissillusionment with Romano would be enough to put him in her camp--and in this instance she was right. Had she not threatened to slaughter hundreds of thousands of Capellans, he might have stayed out of it, but Candace (hoped she) knew which side of the fence he would come down on if push came to shove.
MA