Indeed, Margaery did not suffered the Cersei's humilliation. But I think it was because of Randyll Tarly's arrival at King's Landing, I mean, we all know how much fear and respect many noblemen have for the Lord of Horn Hill. Mace Tyrell may not be the brightest, but he definitely loves his family, and with Kevan dead and no honorable Lannister (if there was ever such) to guarantee his daughter's safety, he might recall her to Highgarden or with his army, and send her away from Cersei. With Cersei in power, the Lannisters will go into utter decline! So House Tyrell might rose once more but this time, at the side of Aegon VI Targaryen. And concerning Tommen, he is a child, his marriage can be annuled anyway. If he is alive or not is a minor factor, we know that Cersei and after her Kevan were the ones who truly controlled the realm. Now we must remember that a hundred swords from Highgarden are the new reinforcements of the City Watch of King's Landing. Could it be that Aegon might take the capital aided by those swords sworn to the Tyrells?