If we're just talking about slate canon here (IE, no loaded save) it is hard to know which side will be chosen. While I certainly don't like to take many cues from this series, the way Mass Effect does save loads allows for freedom without having to play the first game. I would hope you at least get to choose: Vernon or Iorveth, rather than having that forced upon you. Both lead to valid choices (Vernon's side is the most involving in Act 2, Iorveth's only in Act 3) and eliminated the usual towing of the line in the games.
As for the other decisions, they would be the most non-violent. Aryan La Vallete surrenders, Geralt helps Iorveth (Act 1, giving the sword; Act 2, saving him in Vergen), save women (Iorveth's path), spare Henselt (Vernon's path), save Triss, don't kill the dragon (no cure, no kill), and.... I'm not sure what they'd do with Letho. I personally let him go the first time, and I can't be the only one. I imagine though that, since he's the big boss, most would have killed him.
I hope that all of our major decisions catch up with us in some way, rather than being whitewashed like some in TW1 (and some even in TW2!). Of course I want to meet new characters and explore new horizons, but I hope for what we've done to send echoes through Geralt's world, even if the end result isn't immediately perceptible. The political quagmire we left is brewing, and to see the results could mean a lot for us in the future in terms of the locations we visit.
As for where he's off to, I'd wager to say Vengerberg
which was apparently the home of Yennefer in life. Of course, I think we all fully expect that it won't be as easy as checking in, likely harder of entry than Vizima. The King's place is unoccupied though, so who knows? This would also be a truly new area of the world to explore, in the midst of justifiably unrestful times. That would be my guess as to an eventual location, anyways. Gulet
may also be a possible location, being both the home of Letho and the place where Dandelion and Geralt first met. It would be the bard's poetic duty to meet him there! If you'd like to have a more general speculation, I suggest looking at this map
. Follow down from Vergen (near the middle right) southwards. Other locations include Rivia and Aldersberg.