No one can be a leader for life, true leaders have to prove themselves again and again.
Leadership is not a once-for-all exercise, one has to be at it repeatedly, rather continuously. Simply because problems that require the leader's intervention to resolve them keep popping up in any venture of some import. And since no two problems are likely to be of the same nature, in order to be able to resolve them the leaders have to keep updating and improving their leadership skills. Past successes would definitely build their confidence further, but each new challenge would still have to be met. There is no rest or running away for a leader.