If any additional music is needed I’ve always thought the music from the sky hook battle in the Shadows of the Empire sound track would fit well in the rotj death star battle.
That could work, the last 45 seconds of Beggars Canyon chase cold work also but it’s McNeely and not Williams. It is possible to re-edit the ‘Fleet goes to hyperspace’ cue and change the order of cue to match with an assault of B-wings on the star destroyer. The opening section of that cue is :19 seconds and might be enough for the segment he is inserting.