More good questions, and I'm glad you've asked them.
Yes, fighters can be recalled midflight, and in many cases, it's probably a good idea to do so. Otherwise, you might find yourself losing bombers left and right as they start getting worn down. Fighters also will return automatically to a carrier when they run out of missiles.
Performance is currently much better than normal Nexus even with large amounts of ships on the screen, simply due to the fact that the models have only a fifth of the amount of polygons as the Nexus models.
The Kilrathi Light Destroyer currently cannot harm the Midway. I looked up the ship on the CIC database, and did notice it had a classified weapon. Is this an anti-capital ship weapon? If so, I will work on implementing it and fixing that problem. At the present time, however, the Bordrav only serves as an anti-fighter escort ship with a 5 Dralthi fighter force.
I think I stated this previously, but depending on what you take, fighters can attack fighters, components, capital ships, or any combination of those, depending on what type you take. This is actually one of the parts I'm looking forward to testing. While playing this mission, I came to realize just how important fighters are going to be. Nexus may center around capital ships, but the way Wing Commander works is that everything is done by fighters. Even in something like Nexus, you can't take that away. As I add more capital ships, it's going to be very hard to simply rush out the bombers and head straight for a capital ship. You're going to need to actually run your fighters on sorties in order to succeed. For example, you run into an enemy fleet. They launch a fighter screen, which is going to make it hard for the bombers to survive. You launch your own fighters to intercept. As they are going at it, you launch several more squadrons of fighters armed with anti-radiation missiles. While the fighters are busy, the wild weasals will start their attacks on the enemy ships' turrets. This will make it easier on the bombers, because (A.) they won't get shot at and (B.) the torpedoes won't get shot down. Meanwhile, your fighters are having to land and rearm, so you launch another fighter screen to cover them while they reload, and on it goes until one of you wins. Going back to the performance question, even with so many fighters on screen, I honestly don't think the game is going to slow down all that much. The fighters are only around 300 polygons each, as opposed to Nexus' 1500 polygon fighters. Furthermore, the game uses mip maps, meaning the textures will be reduced in quality the further away the camera is from them. Finally, the game will also switch off the bump, reflection, and specular maps if the camera zooms out so far that the extra detail isn't noticeable anymore. With these optimizations already built in, the only way I think you'd hit a performance problem is if you took 16 Midways and launched all 252 fighters from each at once. Ok, you may notice some slowdown before then, but nothing to make it unplayable.