MC knows the anti-magic device exists, so one would assume he thought about countermeasures during the decade he was trapped inside the sarcophagus. Though that being said, if he has any wits, he will just make himself scarce right now, to return later when he's in full physical strength and has made ample preparations. When I say return, I don't mean this city but he would keep striking elsewhere in the empire for a number of years, where the military expects it the least. After the capital itself started to feel more safe and secure after years of inactivity, only then return there.
He would also need to drop the remote transfer satellite from the orbit.