Here's a thought exercise. I think we can all agree that giving the orb to Cory was NOT GOOD.
What would have happened if Solas *hadn't* given the orb to Cory?
No explosion, right? Right. Would the mages and templars have stopped their war? Maybe. If yes, no Inquisition. If no, Inquisition gets formed with Divine Justinia backing it to stop the mages and templars - at least so Cassandra implies.
Cory doesn't just disappear. He's still planning to take over and make himself a god. He has the Venatori. He has the red lyrium. He probably even has the Grey Wardens. Most likely, he's STILL planning on assassinating Empress Celene and invading with a demon army. He doesn't NEED the orb for any of that. What does he need the orb for? Entering the Fade. What does he do without the orb? Looks for alternate ways to get there.
Without the explosion at the Conclave, no one knows what Cory is up to. No one even knows Cory exists. Cory is pretty much free to do whatever because no one is trying to stop him.
Obviously a great deal of this is conjecture, which is why it's an exercise in thought.
So, what does everyone else think Cory would have done without the orb?
He might have gone after elven ruins, but he wouldn't know about the Temple of Mythal or the Well, as he gets that knowledge from the Orb.
He probably would have played it low-key, maybe built up the Venatori to re-do the ritual that sent them into the Fade. Though I got the impression each of the Seven Magisters contributed their own gods' secrets to the rituals, and they strained themselves to make the ritual work without revealing too much of their own knowledge.
Hmm. Part of the Mage-Templar conflict's worsening is because all of the people willing to parley were crispy-crittered. But it's left ambiguous as to whether either side was willing to concede anything. I think the Inquisition would have formed with the advisors and Cassandra, with Justinia at its head, and there would have been some zaniness. Meanwhile, Corypheus can probably still get Nightmare on his side to go through with the Warden plan, but the Inquisition doesn't have the impetus to head after them.
Really, pre-game and end-game, Corypheus would have been served so much better by working from the shadows.
*glances at rumors of centuries of blood magic influencing the Grey Wardens at Weisshaupt from Last Flight*
*shrugs*