Sasuke knows that Tobi isn't Madara. It was confirmed to him when Tobi tried to show his face to Sasuke after the Battle between the Uchiha Brothers. That would be simple to think "for Sasuke", Why would Madara hide his face if he barks to him about his identity?
He assumed that Itachi understood about the Edo Madara and ran off to cancel the Edo Tensei so as to stop Edo Madara to create chaos.
But even Itachi didn't knew that. Here's the reason
Itachi would have had said to Naruto that,
(After sealing Nagato)
Itachi : One more thing Naruto.
Naruto : What?
KB : ....
Itachi : When I was in Akatsuki..... being knowing that the mask man is Madara, I suspect that....he's not.
Naruto : What?!!
KB : ?!!
Itachi : Since you'll be facing the mask man, I want you to be aware of his space time jutsus. I didn't get into combat with him that is why I do not know much of his weakness either.
Naruto : (a detective face) Hmm. We'll soon know it. (thumbs up to Itachi. Itaachi moves on to cancel Edo Tensei)
That's why Sasuke was calm after knowing Edo Madara's existence even after ET is cancelled.
But since Juugo can easily communicate and grab the news online through the birds flying away from Edo Madara (the creator of the destruction) as well as due to his clans abilities of sensing people, Sasuke got the news.