IMO, The GRN should overextend their war effort, the council / maquis should sweep in and dethrone the current leadership and establish a house-wide coup, planting a new elected official on the throne. GRN/GRP forces should be split, with most accepting the new leadership and being pulled back to Gallia, while a few stragglers support the dethroned monarchy and become renegade exiles with no infrastructure to fall back on.
The council, now in control of gallia, opens up foreign relations to the other houses. They pay war reparations to Bretonia and Kusari, and all gallic holdings outside of the Tau systems are given back to their respective owners, with council-led efforts by the GMS/IDF/EFL to repair and restore any infrastructure destroyed by Gallia in other houses.
The entire gallic military fleet is officially disbanded, with all warships that are still in serviceable condition being relegated strictly to operating inside gallic-owned systems in a defensive / anti-criminal capacity, including seeking out renegade ex-GRN/GRP exiles and putting them down. Gallic Corporations who remained loyal to the Monarchy and supported the invasion of Sirius are all heavily taxed by the new government, with those funds being distributed as reparations to Bretonia, Kusari, and all refugees and factions adversely affected by the war.
Non-military gallic technology is opened up to civilian use throughout sirius without restrictions, as gallic corporations search for new sources of income. Military gallic tech is opened up for purchase by lawful military, police, and intelligence entities within Liberty, Bretonia, and Kusari, and the Core, meaning 100% tech compatibility for those factions with gallic lawful equipment. Council/Maquis equipment becomes civilian-grade, barring warships, and council/maquis warships are repaired and restored to be used by the new lawful institution.
The Core is contracted by the Council/new gallic government to serve as a police force outside their borders in the tau systems, as all gallic warships are restricted strictly to gallic space. This gives the Core a new area to build their influence, and a new staging point for dealing with the outcasts.
Bretonia, having annexed omega 49 and surrounding systems and now getting back leeds/new london, begins rebuilding and absorbs Gran Canaria into it's house territories. Bretonia, despite rebuilding, is still fighting a border war with the Coalition in the Omegas, along with the Corsairs.
Liberty extends its influence back out into cortez, establishing a new border control there and increasing security around planet curacao so that Orbital Spa & Cruise can re-establish its operations.