From what I have read, I believe that open dialog will serve everyone best. Even if one is contemptuous, it is important to emapathise with them to best see their persepective. Consider the roots of the problem and tend to them, not the leaves. If the former head has truly stepped down, how is he re-instated as lead practitioner without the approval from your sensei. Has this person considered the feelings of your active sensei. This former head may have a following of loyal students who wish to follow, but certainly yours does as well. Could these two institutions co-exist. Many schools of thought diverge from a single source to emphasize what is important to them, yet they share commanality throught their shared roots.