Just read Thor’s great suggestions for house-ruling fleeing during a kill conflict (https://www.burningwheel.com/forum/showthread.php?15445-Fleeing-from-Kill-Capture)
What about the reverse? If you’re fighting a big mob of creatures (e.g. a band of Kobolds) can you initiate a primarily Drive Off conflict but with the express aim of trying to kill some of them as you drive them off, to whittle numbers down slightly. Still fits the narrative, seeing some of their comrades killed will surely encourage those pesky Kobolds to get running! Presumably you would you narrate this based on the level of Compromise at the end of the conflict? Perhaps going harder on the PCs - in return for killing a few Kobs, the players should expect to have more onerous Conditions to be applied to them?