Butler is a guy like most who will need to win a spot on his team every year. Very few guys are sure fire slots on a team. His chances go up or go down depending on his chemistry with Dak, is he a hard worker and his salary demands.
He, like most players, will play for a few years and then the league will replace him with someone younger/cheaper. Knowing nothing about his character, I wouldn't call him a bum. He has found a way to have a 5 year career or so (with maybe a few more years if he is lucky). I also believe he even started or completed a master program in college. Fringe player but the league is filled with them.