Sure! But if the impending dooms of both dangers should come true, the result would be the same: Oronx. Oronx EVERYWHERE!
Sure. It's your job to threaten them with it. It's up to them to change the course of things. But given their history with the Order, that's something the PCs aren't likely to want to see come to fruition. Healthy doses of Signs of Doom and their witnessing the progression of Grim Portents should make it enough to encourage them to step in, or deal with the consequences, especially if they're directly affected by being rounded up as one of the heretics, as they were previously accused.