Redmine

https://github.com/redmine/redmine/blob/master/app/controllers/members_controller.rb

def destroy
    if request.delete? && @member.deletable?
      @member.destroy
    end
    respond_to do |format|
      format.html { redirect_to_settings_in_projects }
      format.js
      format.api {
        if @member.destroyed?
          render_api_ok
        else
          head :unprocessable_entity
        end
      }
    end
  end

https://github.com/redmine/redmine/blob/master/app/models/member_role.rb

  def remove_member_if_empty
    if member.roles.empty?
      member.destroy
    end
  end