Dead Orbits presence in the Tower is questionable at best. How did they keep themselves from being thrown out? They made themselves look useful. They told Zavala about the transmission. Under Zavala's order and HIS order alone (Not Dead Orbit), they set up defensive lines. Their fleet wasnt on standby. It was being prepaired to flee, as always. Commander Zavala gave the order otherwise. If Dead Orbit argued or refused the Titan Vanguard, they would have lost any chance of staying in the Tower and sponsering Guardians as a Faction. They also would have lost their most lucritive resource intake. They didnt do it to save the City. They did it to help their cause and prevent them from being kicked out. What they did changed nothing.