There is no answer from Lanzar; no further communications.
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Which is actually indication of Rebel failure. Better diplomatic efforts from the Rebels could have caused a considerable diplomatic coup for them at this point, but instead the Lanzar silence, whilst defiant, is merely incriminating.
This brings to an end the political phase of the game. You have clearly won- war is on Lanzar, in the Emperor's time limit, and without any Senatorial hassle. Oh, many Senators will debate and question, but the fact that they really did try to kill you, so soon after a political settlement, means that nothing will come of it, not even from the most virulently anti-Imperial Senators.
Sartorus- who was not trying to kill you, btw, though he did have it in mind that the Guild leader would try something stupid- has got pretty much all he wants. You can live with that. Your means have been brute forced through, and as the Rebels neglected to oppose you on that front, it didn;t need to be any more clever than that.
There are a few things to tie up with the Rebels as they try and salvage the diplomatic situation- and then it is war war war!