I actually posted this first in an other thread but I decided it would be a more interesting subject to talk about in it's own thread.
I was thinking today, with the battle of winterfell at the end of adwd/begin of twow roose is in a very dire position. Assuming the pink letter is fake he has some options still left to him. Like winning the battle, fleeing (which is very unroose) or what I was thinking of earlier today. Trying to go over to Stannis' side making the necessary "sacrifices". The main scheme of Roose is having power and making sure his family name survives. Although he does not want a "child lord" as it's the bane of every house. I think that to survive he will have to let the last go.
The reason for it is as follows :
Many northeners hate Ramsay and hate Roose because they think he killed Robb. I think Roose actually has more of a long term plan once Stannis besieges Winterfell. I think chances are Roose might parley with Stannis first before a true battle would occur. It might even be that roose would traverse the ice alone to speak to Stannis. (Maybe even bringing him some sort of sign of goodwill)
Keep in mind, Robb was Stannis' enemy. Roose actually "helped" Stannis by killing Robb he might actually try that to get atleast some form of amnesty. I think Roose might try to convince Stannis that he killed Robb for the "good of the realm" because he would have destroyed the seven kingdoms. He might even be "reaccepted" by other northern lords if Roose brings Ramsay to Stannis and return all northern captives from the red wedding. He might also try to convince Stannis even more to bring the bolton men into Stannis army (of which there is still a considerable force), converting to the red god and promising retirement (to the wall??) once the war is done and his son by fat walda frey can get the Dreadfort. Stannis might even be "forced" to accept Roose's offer when the wall has fallen. No one will care then about what Roose has done, that's for after the war and Stannis has often said it in the books. Every lord will get what's coming for him, but if there is need for someone now justice can be done later. (like he plans on doing with various dragonstone lords that desserted him)
I think that is Roose Bolton's plan. Try to switch sides, convince Stannis that killing Robb was the best thing he could have done for the northern situation. That he was hoping that by killing Robb Stark the North would atleast have survived the upcoming winter and not lose their lands to the ironborn (which he has actually prevented, he reconquered the north). I think he will try to make Robb's death a "noble cause" but still denounce house Frey for the red wedding itself of which he was obviously against. He was merely scheming against Robb Stark when he heard that they were going to butcher him at the red wedding. By then it was too late to stop. Or something amongst those lines as a "reason" for doing it at that point.
Ofcourse Roose Bolton wouldn't be Roose Bolton if he wouldn't backstab Stannis later, but that is even the longer term plan. Why would Stannis accept this? Maybe because the wall fell, maybe because killing Robb was indeed a huge boon for Stannis. (he has his army now after all)
To add something. I still think that Roose Bolton might still have some small redemption in this story and I think this is the best point at which he could be redempted.
For the possible gnc believers, this could also be a possible wedge between the northern lords and stannis that could lead to another king in the north although I wonder if the gnc is true.
Tl;dr : Roose will betray Ramsay, will try to join Stannis' cause and the castle will be attacked from the inside by bolton men.