Robb Stark and Moat Cailin (Spoilers Everything)

On my umpteenth reread and I just caught something. When Robb learns of Balon' death, we learn something useful.

“If she stays at Deepwood Motte that’s all she can hope to hold,” said Robb. “What’s true for the brothers is even more true for her. She will need to sail home to oust Euron and press her own claim.” Her son turned to Lord Jason Mallister. “You have a fleet at Seagard?” “A fleet, Your Grace? Half a dozen longships and two war galleys. Enough to defend my own shores against raiders, but I could not hope to meet the Iron Fleet in battle.”

Mallister has enough men to land Robb in the North by way of the Sunset Sea and completely bypass Moat Cailin. Of course, he can't take the 3k+ cavalry he has with him when Mallister comes to him. He can however take a large enough force to see him safe along the stony shore. If the smaller Ironborn longships can carry 100 men, then Mallister should be able to carry at least 800 men (6 longships X 100 men and 2 war gallens X 100 men) and land them North.

It is still autumn at this point and the North is far from spent.

The Mountain clans have 3000 men

Stannis rubbed the back of his neck. “You haggle like a crone with a codfish, Lord Snow. Did Ned Stark father you on some fishwife? How many men?” “Two thousand. Perhaps three.

Umber isn't either.

“The Whoresbane his own self,” claimed a riverman who’d just brought a load of hides and timber down the White Knife, “with three hundred spear-men and a hundred archers.

Whoresbane left with half of the Umber levies

Jon chose to ignore them. “Your Grace, might I know if the Umbers have declared for you?” “Half of them, and only if I meet this Crowfood’s price,” said Stannis, in an irritated tone. “He wants Mance Rayder’s skull for a drinking cup, and he wants a pardon for his brother, who has ridden south to join Bolton. Whoresbane, he’s called.”

Umber can still summon 600 men, although they are green boys and old men.

Manderly still has a strong fighting force as well.

“Perhaps you understand, then.” Wyman Manderly lurched ponderously to his feet. “I have been building warships for more than a year. Some you saw, but there are as many more hidden up the White Knife. Even with the losses I have suffered, I still command more heavy horse than any other lord north of the Neck. My walls are strong, and my vaults are full of silver. Oldcastle and Widow’s Watch will take their lead from me. My bannermen include a dozen petty lords and a hundred landed knights. I can deliver King Stannis the allegiance of all the lands east of the White Knife, from Widow’s Watch and Ramsgate to the Sheepshead Hills and the headwaters of the Broken Branch. All this I pledge to do if you will meet my price.”

We aren't given exact numbers since he only goes to Winterfell with 100 knights.

There are even the survivors of Ramsay's betrayal at Winterfell

From Stannis' letter to Jon

… more northmen coming in as word spreads of our victory. Fisherfolk, freeriders, hillmen, crofters from the deep of the wolfswood and villagers who fled their homes along the stony shore to escape the ironmen, survivors from the battle outside the gates of Winterfell, men once sworn to the Hornwoods, the Cerwyns, and the Tallharts.

Robb North of the Moat could have more than 4000 men. More than enough to take Deepwood from Asha and march on the Moat from the north. Of course, George had to write it so Robb would die, but this could have been infinitely more interesting for the story if he lived and made it home.

It would introduce a whole new dynamic once Stannis comes North and Joffrey dies at his wedding then Tywin dying by Tyrion's hand.

Robb still isn't going to win the war, but it would be interesting.