It's a buggy mission even with the patch.
Try and take out the ISD's guns (especially on the side facing the Cruiser). You can pretty much ignore the Interdictor as the other squadrons will take care of it.
Saying that though, even if I manage to save the Cruiser half the time it vanishes into hyperspace never to be seen again...I usually skip this mission.
...A battered and bloody Chewie regained his footing, stood up high on a pile of rubble, and faced the descending moon with arms upraised and a defiant roar.