Not so much how the actual plate would be made, but moreso how it would be aligned with the motion of the rest of the shot. Sure they had motion control but the plume would obviously not have been to scale with the rest of the elements, as such the previously used camera moves wouldn't have worked. I imagine it would have taken a lot of time to integrate them properly, and it would have also introduced yet another generation in to an already composite heavy scene.

These sort of things were usually animated by hand or they were very simple shots. Jedi has impact explosions that match motion during a shot but the motion is slow and simple.

To clarify the above applied to the first plume (which has a good amount of motion). The following plumes are on a stable shot.

Few more observations:

-After the collision the right TIE makes several rotations before colliding with the wall. Given the inertia of the ships before the collision, this motion doesn't seem to make a lot of sense. But I'm only commenting on this because I used to animate; it's a very minor point in a well executed shot.

-After the TIEs collide, the camera slows or stops for the last few frames of that shot.