Senior staff have already proved themselves by getting the job haven't they? Many Heads, DH and AH do teach and others work alongside staff to support improvement and can facilitate improvement by having an overview of provision across the school. Also a coaching style is all about the Teacher in question finding improvement from thier own reflection. You don't need to have a class or teach regularly to support classroom improvement. If you can find time to teach it is great to do so as it is enjoyable. As a senior teacher all you want is the best for all the children in the end.