Who stands with Cersei? The Mountain, an ex-maester, and some little kids?
Dorne and Highgarden back the Dragon. The North and the Vale are behind TKitN. Baratheon is spent. Frey is leaderless. The people of Kings Landing probably hate Cersei.
The Lannisters are down to Cersei, Jaime, and the Hand of the Queen. I feel like the Lannister army will follow Jaime. i don't think Jaime sticks with Cersei.
I certainly see an opening for a crazy pirate to marry into the Iron Throne.
As for Dany, it should take 1 episode to retake everything south of the Neck. She has 3 dragons, at least 100,000 troops on boats or already on ground, plenty of supplies, and Sand Snakes.
Is LittleFinger unaware the Dragon returns?