I rate Tom Harley very highly. Remember when he was on the footyshow? He never once resorted to the unintelligent toilet humour that a lot seem to get carried away with on that show. The whole time, he portrayed himself as
a true leader. Crawford's antics on that show are why he will never be seen as a true leader at Hawthorn. Although someone mentioned Jonathan Brown before, although he is a good player and leads by example on the field, he too lowers himself at times on the footyshow, and I would not consider him the greatest of leaders of men.
In response to the initial post, I believe Harley will be captain until the day he retires. It's not often that Geelong is sitting on a premiership captain. They wont be desparate to push him out the door. As someone else mentioned, Selwood looks to be a good replacement, and I believe the club will groom him for the position over the next 4-5 seasons. I don't see him taking over as captain at least until he is 22-23 though, and if Harley departs early I'd like to see Chapman or Scarlett as captain.