What if Robb won?

[UFT]

lets say he made all the decisons we think he should have made (theon stays, karstarks stay), and king's landing falls.

what would he do next and how would it affect the rest of the timeline/country?

 

[Daena the Defiant]

11 hours ago, UFT said:

lets say he made all the decisons we think he should have made (theon stays, karstarks stay), and king's landing falls.

what would he do next and how would it affect the rest of the timeline/country?

Well, lets just handwave away a lot of the circumstances, errors in judgment and the Intended Doom that the Author Intended and start to kick around this idea.

In your scenario  for Robb to have won the Freys have to stay on board so that means that Robb honors the pact with Walder and takes a Frey wife (I'm assuming that Roslin is the pearl among the swine that Robb chooses). The Riverlands stay firmly in his camp, allowing Robb to effectively check the Lannister influence. Is Margaery still on the market? She would be a suitable bride for Edmure. Otherwise, the Highgarden/Storms End alliance is still going to happen and is still going to be a major problem to any settlement. Both Baratheon brothers still consider the Baratheon claim valid (even if the Lannisters have been scrubbed from the capitol). In your scenario, who actually is the successor to Joffrey? Stannis or Renly? 

King Stannis is certainly not going to accept losing two of the seven kingdoms in perpetuity. If he can bring Highgarden and Storms End in line (assume he still assassinates Renly via Melissandre's shadow ninja babies), and then uses his kingly powers to dispossess the Tyrells via attainder to award Highgarden to his in-laws, the Florents, Robb has a massive problem on his hands. 

King Renly and Queen Margaery would probably be more cavalier about the existence of the Kingdom of the North, as long as Robb stays in his lane, possibly attempting to orchestrate some sort of loose feudal submission. Listen, you can yourself whatever you want, as long as we all pay taxes, don't try to topple me and we all still use the common coin of the realm. In time, perhaps some sort of marital alliances will work to knit the Riverlands and North back into the overall network of the Seven Kingdoms. Sansa would be a suitable wife for Willas, and would become one of the great feudal matriarchs of the continent in time. I'm assuming that if Renly has prevailed, Stannis is dead, so perhaps King Renly attempts to broker a marriage with Shireen and Rickon (who is younger), for the governance of Dragonstone to help cement the family ties. Arya perhaps could end up with some higher tier Baratheon or Tyrell vassal.

It is entirely not within his character for Robb to attempt to take the Iron Throne himself. Let's assume that he goes whole hog megalomaniac and does. He is going to have devise a way to subdue the Storms End/Highgarden alliance (Renly) and Dragonstone (Stannis). His court will be crawling with Freys, alas. Catelyn (since we won the war, her decision making must be more successful) will be given a powerful advisory (although probably informal) role, unless she is sent back to Winterfell to rule in Bran's name in a regency capacity.  The Stark/Frey regime is going to have enemies at all sides. Robb could attempt to entice Highgarden back into the realm by offering Sansa to Willas, but from Highgarden HQ's perspective, having a Tyrell daughter be Queen is better than having a Tyrell son be the king's goodbrother, so that's probably not going to be effective.  I predict another massive civil war. 

[Ralphis Baratheon]

Robb was doomed as soon as he was named King of the Trident. He simply didn't have the resources or men to hold the Riverlands. He would have been fighting wars his entire life to hold the Trident.