“They've always been aware of the forbidden prince. They are all aware that the prince has been 'firmly confined,' but what happens when the prince who is supposed to be firmly confined escapes?”
“People will be terrified of the prince's authority. In the meantime...” Cass' eyes flash with uncertainty. “...Faith in the high authorities will be eroded, and people will be outraged as to why they did not kill the prince in the first place.”
One reason Salzaal is still alive is that he is royal, and the queen is descended from the secondary Lancelot lineage.
Even the Gawains, who have been at the helm of the round table council for generations, must now defer to the Lancelots. Salzaal is descended from the first and second most powerful people, so he does not have to die right away even if he possesses the dark power.