They could become more sympathetic. For example, they might realize how small and fragile their world is compared to the large - scale war of the wizarding world. This could make them less cold towards Harry, as they see that he is part of something much bigger and dangerous.
The Dursleys could also be forced to confront the wizarding world more directly during the war in fanfiction. Maybe they have to deal with wizards seeking refuge near their home. Dudley might even start to have a different view of the wizarding world, which was always so strange and terrifying to him before.
Harry would probably be nervous. He's always had a difficult relationship with the Dursleys, and having his girlfriend there adds another layer of complexity. He'd be worried about how they'll treat her and how she'll react to them.
Fanfiction often shows the Dursleys' relationship with Harry as complex. Sometimes it explores how their fear of the abnormal, which Harry represents, drives their actions. They may be cruel not just out of meanness, but out of a deep - seated fear of the unknown magic world.
One possibility is that there could be a very tense encounter. The Dursleys have always been unkind to Harry, and after the war, they might be even more resentful or fearful. They could try to avoid him or act coldly.
Well, it could be that the Dursleys are still as cold as ever at first. But Harry, having grown so much during the war, doesn't let their attitude affect him. Instead, he just calmly states his new life and how he has moved on from their influence. Maybe this makes the Dursleys start to see him in a new light and gradually change their view of him.
It's possible. In some fanfictions, authors might explore complex motives for the Dursleys' actions. Maybe they could be under some dark magic influence that makes them act out of character and in a more extreme way. However, this goes against the general perception of the Dursleys in the original series, where they are mainly just cruel and neglectful without such extreme murderous intent.
Often it could be the magical community. Since the Dursleys have mistreated Harry, a wizard, for so long, the Ministry of Magic or some powerful wizards might decide to teach them a lesson. For instance, Dumbledore could use his power and wisdom to make sure they face consequences.
The relationship between Harry and the Dursleys would likely be very different. Harry has faced so many challenges during the war and has become more confident. He might not tolerate their old ways of treating him. For example, if Uncle Vernon starts to yell at him, Harry might simply walk away instead of getting angry like before.
Well, Daphne in the 'Daphne meets the Dursleys fanfiction' would probably interact with the Dursleys in a very cautious way at the start. She would be observing their behavior towards Harry closely. Once she realizes the extent of their nastiness, she could try different approaches. She might try to reason with them, explaining how wrong it is to treat a child like that. When that doesn't work, she could use her magical abilities to disrupt their daily routine in a harmless but annoying way, like making the TV constantly change channels or the kettle never boil. This would be her way of getting back at them for their treatment of Harry and also a way to show them that there are forces they don't understand.