Can there be leaders without followers?

I think not. I don't know how that is even possible. Every leader has at least minimum of followers in the terms of assistants, co-workers, business associates. Without them, the leader wouldn't be on that position.

Plus, if there are no followers, leader can't be a leader because there is no one to be led and no one to vote/choose him/her for the leader. Followers are those who maintain the leader's position in some way. They give their faith and trust in him/her by cooperating together on important issues.