I currently think our best bet, and the plan we should present to the High Council, is as follows:
1. Avernus does not deploy anyone against Waaagh Bear.
2. The rest of the Trust deploys against Waaagh Bear.
3. Ideally, the Crusade will come attack Avernus, at which point we will harrass and turtle, allowing the Avernite wildlife to attrition the Crusade down.
4. If the Crusade deploys Astartes, the VG will deploy to Avernus instead. Enemy Astartes are capable of breaking a siege by acting as special forces, and we don't necessarily have high tier enough units to stop them if they deploy a chapter or more of astartes.