That's the starting assumption that was voted on, yes — that the cure could result in exterminating 3/4 of the 'population,' but also free the actual living from their current illusion of co-existing with the undead and possibly reuniting Eidris and Minaras.

You're welcome to have him get in touch with the leaders, if you want to take that path, although I'm not sure how he'd prove it to them! But I'm sure he can get creative.

That said, as a reminder, there has been indication that at least one leader (Arabella) might unknowingly be a mannequin. Nothing has been discovered either way about Thivar so far.