Time travel to the past is a bit of a cop out, but I can still see it happening.
My theory:
The plan is for the Discovery to scan Qo'nos from the inside while an away team, for whatever reason, partakes in some undercover mission on the planet surface. Captain Mirror Georgiou is a rogue variable in this entire situation, but I wouldn't believe she would betray or harm Michael. L'Rell certainly has more to do as well as House Mo'Kai with its leader Dennas, and perhaps they attempt (with Captain Mirror Georgiou's gentle persuasion) to pacify the Klingon houses. Their attempt fails (or perhaps L'Rell rats out Discovery) and a Klingon fleet enter Earth's orbit. Things become dire, and Admiral Cornwell and what remains of Starfleet command ponder over the choice to destroy Qo'nos as a last ditch effort to stop the Klingons and end the war. Michael vehemently objects. Captain Mirror Georgiou, a woman of her word, makes the decision to annihilate Qo'nos and attempts executes it. The crew of the Discovery, or perhaps just a stubborn few, mutiny again the Captain, but it's too late and Qo'nos is on the quick path to destruction. The orbiting Klingon fleet, in retaliation, destroys Earth. A last resort, now that both homeworlds have been destroyed, is attempted either in haste by the Discovery crew, or in mutual agreement with the Klingons ("Will You Take Me Hand?"), to travel back in time to avert the war and its devastating casualties.
Or not, I dunno.