There will always be a need for resolving interpersonal conflicts in workplaces. HR though predominantly exists to protect the company from any liability and secondly to maintain the hierarchy and retain the labor it values the most.
Conflict resolution under socialism could be much more humanistic, focused on actually resolving the conflicts and getting the best outcomes for workers. However nothing will ever be perfect, sometimes conflicts will not be resolvable, the truth of circumstances unknowable or some people truly indispensable so I imagine there will still be instances where justice is not accomplished. Though under socialism at least you would not be as dependent on your job just to be allowed to exist and therefore considerably more free to hit the bricks if shit sucks.