If there is any conversation at all with Darl Quethos, I'm sure my party will try to explain why stopping the age of worms is more important than getting his eye of vecna. And if I were Quethos, I'd find that pretty compelling. Why would he want a world full of Kyuss zombies? He'd have to be pretty crazy, and thus far he's seemed pretty smart.
The alternative would just be for him to attack without giving anyone the chance at negotiation.
One thing that occurred to me - why not let Quethos get the location of Dragotha's phylactery, use that to trade for information, and then give this knowledge to the players too?
