Its essential to replace yourself.  At high school I led the Science Society, the History and Geography Society and the Music Society (a highlight being to present Fanny Waterman, piano teacher and a founder of the Leeds International Music Festival with a bouquet of flowers).. I love leading groups like this. 

One of the things I didn't learn there was to replace myself - it  wasn't necessary - there were plenty of people ready to step into my shoes.

However, in life if you have a job, its essential you groom a replacement fairly quickly and move on to a higher role.  This is one way to get promoted.  I did finally work out how to ask for a promotion after 4 years at the same company - but I wish I'd figured it out sooner.