Maybe Rip is a procrastinator like Hamlet.
Look at all the things Hamlet does while putting off the inevitable. He writes and directs a play, he watches a general go off to war, he escapes his abduction to England and conspires to have Rosencrantz and Gildenstern killed there, he digs through bodies in a graveyard, he yells at his mother and kills Polonius, he drives his girlfriend mad to the point where she kills herself. If Hamlet had just killed the king, he would have never created all this other drama.
Rip might know what he is destined to do to ultimately destroy Vandal Savage, but in putting off that final act he's getting a lot of other things done.