You can talk to some people until you are blue in the face, it won’t change the fact that you have a definite personality conflict on your hands. It isn’t your job to get inside your players' heads and be some kind of baby sitter for their “inner child.”
There is a mantra that experienced gamers will acknowledge: In a contest between the Game Master and the players, the players lose. Every. Single. Time.
I say killing him is okay… but have fun with him first.
Start by stripping his power: break his favorite weapon, lose his spellbook, or whatever.
Then have his character fall into deep water. As he starts sinking – fast, explain that he has a choice: either he must jettison all of his equipment, or he drowns.
When he gets back to town, have all of the local villagers harass him. All of them. At the same time, the villagers extend the usual courtesy to his party members.
Have a doppelganger pop up and start destroying his credibility by committing heinous crimes. Make him a wanted man, and encourage his fellow party members to turn him in.
In short, destroy him (thoroughly) before you give him the luxury of death.
Then raise his character. Bring him back as an NPC, and have him become the antithesis of whatever his character used to hate. If he was a thief, make him a perfect paladin. If he was a fighter, make him a healer. You get the idea.
If you allow “Bob” to re-join your game, you can even bring this character back to become a recurring menace to his new character – and only his new character. The rest of the party may not even know about (or even believe in) this mysterious pursuer who seems to lurk around every corner.
OH, the possibilities. And at the same time, you instill the fear of GM in the players. It’s a win, win situation! (Except for “Bob”.)
But then, some people accuse me of rooting for the bad guys in all of the Bond movies, too. Go figure.