Sejuani's Destiny
Gonna get right to things, looking at the current state of the Freljord lore (in its weird-ass state) there's only a few paths I can see Sejuani's character taking.
-
One of the not-so-likely scenarios is that Sejuani wins a war in the Freljord. I do not believe that Sejuani could win a war on her own against both Ashe's and Lissandra's factions. In order for her to win this war she would definitely require outside aide. This aide could come in the form of Noxian interference, Lissandra manipulating her, or Volibear going all god of storms. While Sejuani no doubt boasts some badass warriors and groups of people, there is no way that living under her rule as a non-combatant is that great. If she were to win, her reign would not last and most likely fall into civil war and Noxian invasion.
-
Sejuani dies, this is the least likely path because Riot just doesn't kill their champions (which I detest but hey that's just how it is). However, this would fit in with her character a lot, because I don't see Sejuani compromising her values to anyone, let alone Ashe, and her fighting on the front lines is not going to do her any favors in the long run.
-
Sejuani surrenders peacefully, there's no way this happens without existing pressure from somewhere. Noxus would have to be knocking on the door or the Void invasion would have to start for Sejuani to willingly consent to any form of surrender.
-
Sejuani is captured, or otherwise crushed to the point of irrelevancy. What I mean by this is that the Avarosan tribe and her allies crush Sejuani enough that she becomes more akin to a bandit leader than a sovereign head. Capturing her would be difficult to say the least, and I doubt that any sort of captivity would be permanent for her. Either way, the Avarosan tribe becomes the great power in the Freljord, leaving Ashe to deal with whatever Lissandra has planned.
These are just 4 rather vague and abstract directions that the civil war could head in. The overall theme is that Sejuani's ultimate character arc leads her down the path towards villainy, unless she has some sort of about-face on her moral compass.