The Golden company have a card up their sleeve. As I said in post earlier they have a good chance to flip sides.
Team North can call on House Tarly with Sam as their acting Lord. They bent the knee even tho the daddy & bro didn’t. Their are likely soldiers left over from House High Garden. I highly doubt they all got killed. Don’t forget river run and black fish ( even tho no one knows where he is) . Plus Yara and the Iron islands.
Cerise did not get as big of an army that she was hoping for.
What about the 2nd sons? That team have been sipping on pina Cola’s on the beach.
there may be the Tarly's. The black fish was killed when the lanisters came to retake river-run (they report to Jamie that he was cornered and killed while trying to escape), but their forces, and possibly even what Frey's remain, may join the fight. High garden's bannermen may be a possibility too.
There were northern houses that hold up at their own keeps instead of joining the rest. Presumably any of those houses that were south of Winterfell are fine.
As has been mentioned, there's a good chance the Golden company will flop sides on their own, or that the Iron Bank will simply want to be rid of Cersi because she's crazy, and getting rid of her now doesn't lose them any money.
I also expect they'll show a surprisingly large number of human survivors from Winterfell. I feel like every big battle seems to have way more goons walking away unharmed than I would have possibly imagined, based on the watching battle itself.
They'll also probably be joined by any old house that isn't
super stoked to live under Cersi, even if they're loyal to her now (dragons can be persuasive).
I don't imagine we'll see the second sons. There's no fleet of any sort to bring them.