If Robb Stark had not married Jeyne Westerling, how would that have affected the outcome of the war? Of course, the Red Wedding would not have happened. But even then the Stark-Tully alliance would still be outnumbered at least 3:1, and Lord Frey would still be looking for a way out, and the Boltons would still be sharpening their knives waiting for an opening, not to mention the Ironborn in the North.

It’s important to divide the Red Wedding from Jeyne Westerling – Roose didn’t care about the wedding, he wanted the North. And Roose did far more damage than Walder did, when you add up the losses from Duskendale and the Ruby Ford. 

However, there is an issue of timing here. As best as we can tell, Robb died the last week or so of 299 AC. Things were already looking up for Robb with Balon’s death and the withdrawal of much of the Ironborn from the North.

If Robb can survive another week, Joffrey’s dead. 

If he can survive another month, Tywin’s dead.

And after that, a number of things start cropping up that would make it very difficult for the Iron Throne to bring their full weight to bear on Robb Stark. First, Euron’s invasion of the Reach is going to draw large numbers of Tyrell troops away from the Riverlands. Second, once Cersei starts feuding with Margaery, she’s not going to have the Tyrell troops 100% at her command. Third, there’s still going to be the need to occupy the Riverlands and besiege Riverrun and Dragonstone and Storm’s End – which spreads out the forces she does have. Fourth, Connington and the Golden Company will land in the Stormlands. 

So I think the numbers are less telling than they first appear.