Combat and campaign are two games that don't play nicely just yet. You seem to suggest adding a third layer, which might just make things more complicated
Campaign should just be a zoomed out version of combat, but this is impossible due to performance limitations etc. I suggest the following instead, also maybe impossible since the game chokes when you turn up the battle size setting:
Whenever one fleet 'hits' another after targeting it (obviously nothing happens when they just pass over each other as neutrals or whatever):
There's a quick dialogue giving options to talk (transponder fees, inspection, bribery, etc) or fight (as I discuss in the
ambush thread having the outmaneuver option is lame).
SpawningIf you choose fight, then every ship in both fleets spawn rather close in the middle of a large, round map, entering at the speeds and vectors they were on in campaign map. (formation determined by order in the fleet window)
Retreating Ships retreat by going to any edge of the map, and spawn as a separate baby fleet or fleets in campaign. They spawn on the campaign map a little distance away from the main battle in whatever direction they left the battlefield. Ideally, the campaign map would keep going at a much reduced rate (like 20x slower or something) during combat, but this isn't essential.
After battle regroupingThe attacking fleet decides which if any of the retreated ship fleetlets it will attack, or tries to regroup with its own retreated fleetlets. The losing fleet, if any is left, runs away or summons its own retreated ship fleet(s). Maybe combat or a chase ensues, depending on the results.
Needless to say, if some of your ships retreat and after the combat are caught by another enemy before you can join that combat, that combat will autoresolve.
Makes combat more tactical/ interesting.So retreating is dangerous, and its a good way to lose a ship, because if a valuable freighter retreats, the enemy
(if he sees it) could retreat one of its own frigates in the same direction, which could then catch it. So everyone is incentivized to keep their fleet together, rather than retreating ships, and form defensive lines around civilians, etc. It would make combat a lot more tactically nuanced..