In my campaigns, the upper planes are not all "Peaceful" they are "aligned" and lots of emotions are possible. Every alignment has people who engage in combat. It does not need to be evil or to the death.
The Upper Planes can have regions where people can test their mettle in non-lethal ways, whether via duels, skill challenges, puzzles, scavenger hunts, and other ideas. Fighting someone doesn't mean they will kill you. Maybe being defeated in a certain areas cause you to be sent back, and one would have to start their quest all over again, if it was even allowed.
My Outer Planes have "Dungeons" that are challenges to earn experience and rewards, and the good ones may or may not be lethal to mortals, depending on the theme.