Are you sure the internet is talking about Thrinn?
And not the Duergar elder Brithvar (i think?).
The only way i can think about to save Thrinns life, would be to rest twice ... let Nere to choke to death, and Duergars (and slaves) leave the area.
But that is quite certainly not the option you are talking about.
Anyway this conversation is quite certainly another case showing Larian poor writing skills.
Too many options lead to exactly same outcome, and some options are totally absent, as if Larian writers were either unable (or unwilling?) to imagine such option ... or deal with it.
Just as with Astarion. :-/
Just as with Shadowheart. :-/
Just as with Tiefling kids. :-/
Just as with Kagha. :-/
It kinda pisses me off, that we are not able to turn Nere words against him ...
I would like to see option to persuate Duergars that if there wasnt for us, he would be still traped and choking on poison ... and since he demand trial by "letting the Absolute help us", to proove we are True Soul ... i call him being judged unworthy.
Same with Brithvar, if you dont make deal with him ... he specificly coments out loud that he will fight for anyone who will pay him. Why do we have to fight, and dont have option to offer him some coin to support us instead? Or even better, try to persuate him that Nere didnt pay until now, and he would most certainly not pay afterwards either?