Ha ha, look at you guys, thinking anything you did in the Witcher 2 will actually impact the Witcher 3.
We've all played enough games to know how it plays out, here's how I predict it-
Sided with Roach and saved the whole kingdom of Tameria- You get a Blue Tameria Jacket!!1
Sided with Ioverath and saved Saskia the noble dragon and got all magic users raped and killed- You get a package from Saskia! +1 HP candy inside!! Also, perhaps a minor character will make a 1 line comment on what happened!!
As for what's going to be the default starting point that all endings sort of flow towards- well, I'm assuming it'd have to encompass all possible endings, so I would say it's a situation where the whole of the north unites to one army (with your help?) and there is absolutely no weight, on the greater scale of things, to whether "Kedwan took over Floatsome", "Radenia took half of Tameria" or any of that, because they will all act as one big army anyway.
No disrespect though, great analyses, just thought it'd be funny to put forward the cynical perspective.
You never see Roach or Ioverath again.
Also, remember your forgotten vran sword of awesomeness? It does 5 damage now.