I was playing rebel in a recent game and the title situation came up.
I attacked a system containing a DS, super SD, and four TIEs with 2 Mon Cals, 4 corvettes, 2 xwings, and 1 ywing.
After round one, I had 1 ywing left, so I played Death Star Plans, rolled, and destroyed the DS.
The Super SD took 5 damage. And I had the firepower remaining to kill it in round 2.
With the DS destroyed, could the rest of the fleet then retreat?