I get the impression that Zenos is deliberately going to refrain from getting support from the imperial capital simply for the sake of keeping things interesting.

Realistically, they probably have more then enough potential reinforcements to stop the rebellion dead in its tracks, but I think any retaliation from Garlemald itself is likely to occur in the aftermath of the 4.0 MSQ, and will be what spurs the two nations into declaring a full-on war against them, as it's likely their only hope of gaining a lasting peace.