Spotted by Walterion in https://youtu.be/PXiTksRHzxQ?t=15720 , and I could reproduce it myself

In the final dialogue with Vals Varano, you have to click on the "drafted the terms" topic, then select the "Why shouldn't I kill you?" choice, then click on "Bthuangthuv" topic, then choose "I bet I could kill you..." -> "Even so, I'm not accepting your terms" -> "No" dialogue choices, then kill Vals Varano and return to Bthuangthuv (no matter how).

If you do that, the Guild members will have no reaction to the Tong's assault and will have the usual dialogue.