So the high level wizard in my game has hired the party to go retrieve the local macguffin for him. Fearful that the wizard will only double cross them, the rogue is arguing to the party that they should instead either destroy the macguffin (an artifact) or banish it to another plane of existence.

Now, their employer is not going to like that idea. And I'm trying to decide if he will either kill someone in the party outright for betraying him (he's actually the only one that's been honest with the party) or if he'll try and actively stop them from following their plan.

He has the means of scrying on them. He has some of the rogue's blood. Or maybe some kind of curse?

Or does this seem as if I'd be punishing the party for trying to jump the rails?