I'd predict some sort of new alliance against the Vishnans, echoing the formation of the GTVA in some ways... Steele could probably offer terms soft enough to achieve UEF surrender, perhaps some degree of local UEF autonomy in exchange for a UEF-GTVA military alliance and overall GTVA governance.
This makes a bit of sense when you think about the greatest UEF victory, the destruction of the Carthage
. It took an immense amount of logistics and planning, and very heavy losses, including three frigates (four when you count the Indus
getting flung into the sun) - all to take down a ship that, however well altered, is still a retrofitted Great War-era destroyer. This doesn't come anywhere near providing a solution for the Atreus
, not to mention the Orestes
should they be actively deployed. So in my opinion, the threat of directly deploying any subset of the superdestroyer force against Earth's defenses could succeed in achieving surrender under any kind of reasonable terms, especially now that both sides would seem to be aware that the Vishnans' interference isn't benevolent. Common enemies always speed things along.
Of course this is all just my speculative headcanon. I'd love to have it replaced with real BP canon at some point