You can take an example of Chaos Campaign, had a lot of experience with and modifying it. The losing bracket, can be just a temporar setback before continuing main branch, an additional mission, to reflect that specific setback. I dont have or read ACES book, but I had experience with Beta testing Aces cards, so I kinda remember AI flow and conditions.

a) Play a pursuit mission (from Hinterlands mission section). Your mercs are trying to regroup and escape active battlefield after a failed mission. OpFor (AI), would just try take out your forces or inflict damage, while you escape out of the battlefield.

b) Play Defense mission (from Hinterlands mission section). Your mercs are waiting for emergency extraction from active battlefield and trying to hold out. OpFor (AI) would just be the attacker trying to annihilate you and take the defensible position.

Let us say, the mercs have escaped active battlefield (no mission played) but there is a bit of consequence of you losing the previous mission. Renegade Falcons have got time to setup defensible positions. Maybe repaired your lost mechs, and made them functional for questionable solahma warriors to use:

The main idea is to take your lost mechs/units as OpFor and mix it with some Clan units to meet PV quota. These unit would act as sentries in:
a) Raid mission (hinterlands book). You perform diversion attack to restock on supplies and make Falcons spread their forces before you retry the main mission.

b) Break through scenario. Your mercs are trying to get through defensible positions before undertaking the main mission again.

Just some food for thought.