A battle group would be picking up consumables, spare parts, munitions. Possibly hardware and personnel. But Imperial battle groups generally keep supply levels high. The incoming battle group is likely just topping up, so the loss of the station and it's supplies likely wouldn't cause much difficulty for the imps. The resupply could take anywhere from an hour to days, depending on how much resupply they need, and how many ships can be accommodated at once.
The Imperials still hold the orbital station, which is a sector supply station, but the imps don't have the ships to blockade the planet. So the system itself is contested, but on the planet the Imperial forces are restricted to their bunker, where they can watch and listen, but little else. Conversely, the local militias don't have the hardware or firepower to force the imperials out of the bunker, so they've laid siege to it, effectively. It'll be a long process before the Imp run out of consumables. Also, the rebels do not control enough ships to control the system, and certainly don't have enough to threaten the station.
Taking out the station is a significant operation. To do it effectively, you'd need large fleet of heavy ships, or a smaller fleet with a large number of troops. Even if all the militias were under one command, you don't have the resources to seriously threaten the station.
