Even raze killing a province that is chained in war takes a number of hits @ 15 / each. If this is a smaller kd, you should be able to use the relations once the war ends to nw drop (if required) and declare them for a nice farm war since typically they will be hostile with you from all the razes. Having a single province RK'ed doesn't usually affect the outcome of a war, but having a nice farm war after could make it all the better for you.