Amusingly, if Aserit attacks them now, Avalon will lauch his coup at home. Waiting for them to call in their forces to trunce Therti weakens them at home and he's been doing political manuevering under their noses so he has some "quiet' allies that'ere waiting for the right moment.  If they do attack Therity he may show up with "reinforcements" for Therti claiming it was all a ruse by Aserit that he didn't agree with.