Crack theory bc why not
Disclaimer, the only proof of this theory is what I think would be cool to see and would lead to some crazy stuff in later stormlight books and idk i don't see a reason why it couldn't happen.
So, Zahel, Vasher, I think he will do the thingy he did in war breaker w the little girl but with the heralds, erasing huge chunks of memory to get rid of their madness (which would probably take huge amounts of investiture but idk shallan could do a heist bit and steal purified dor from the ghostbloods or something) and they, or some of them could become sane again and idk imagine taln being sane and fully capable or omg IMAGINE IF HES THE VILLAIN OF SECOND HALF bc he's righteously raging about what they did with the oathpact anyway idk Vasher hasn't been very present in the books and he's up to something clearly in rhythm of war and I don't think he's in stormlight just as a fun little cameo which I am a sucker for anyway but I think that his arc in the books will be explained and have a conclusion which could be he saves the day but at the same time kind of dooms humanity yet again or at least creates some other conflict for second half. In any case, we're gonna find out and Vivenna is also gonna be there and it will be so good even if it isn't what I just pitched lol. For additional proof(?) we're also dealing with some memory erasing stuff with Hoid and all that so maybe that inspires Vasher or the Radiants to that kinda thing.
Anyways, first ever redacted theory guys, I hope someone is on board or on the other hand you can completely debunk it which is also fun, peace.