Ny way to get back into a relationship with either Yen or Triss after they dump you

According to CD Projekt RED, no Items or Equipment carries over from The Witcher 2 save file.

Only decisions carry over.

Because they made the games for the consoles and they don't have previous save files they allowed for the user to choose the decisions of past games.

So basically there are no differences from importing the save and simulating one by choosing the decisions.

Since you don't quite remember what you did in those Witcher 2 save files I would recommend to you the simulation of one by choosing the decisions in-game, and you will be more aware of the decisions in-game.

No, not all decisions carry over. Only really important ones for the story. The decisions that are made in the Q&A session are:

• Did you kill Aryan?
• Did you choose Yorveth or Roche?
• If you picked Yorveth you'll 2 choices: did you save Triss or break the curse of Saskia? If you picked Roche did you save Triss or help him save Anais?
• Did you help Sile in the Megascope or not?
• Did you let Letho go or not?

Source: vg247

There are some decisions that you make in the Witcher 2 for example: (SPOILER ALERT)

If you killed King Henselt

This decision is not mentioned in the Q&A Session and there are other decisions that are not mentioned.

Best guess: it's an unintended by-product of events triggered in an open world.

I came past the same camp (at least it sounds like it from your description), though on my way to, not from, Oxenfurt. I started fighting the bandits, who were "alone" when I arrived, when suddenly there were three more people around me. Took me a moment to realise they were guards/soldiers who weren't hostile. They "helped me" finish off the last bandit, but got too close and I must've accidentally (cough) grazed one who came too close to that last bandit. He shouted at me to sheathe my weapon, which I did, and they walked off, leaving me to loot the camp and bodies.

So I think that some overlap between fighting the bandits and the arrival of the soldiers is intended in the game (though the bandits weren't particularly difficult, and there were only three I believe), but for the soldiers to completely wipe out the bandits was probably not intended - after all, you want the experience for killing them. Again, I'm guessing here, but maybe you passed the area previously (speeding past on Roach), close enough to trigger the soldiers approaching the camp, but didn't stop to fight. The game has to handle certain proximity triggers, and, given the open world nature of the game, has to "activate" NPCs based on your proximity (obviously they can't all be actively doing things when you're far away). You've need a saved a game from a short time before you encountered this to test/confirm by riding there directly at full spead vs approaching slowly in a roundabout way and seeing what happens.