With the exception of the last 3 games, Gatens has been far more steady than spectacular during his career. He passed some pretty big names on the scoring list the other night (Brunner, Nelson and Woolridge), so you can't that away from him.
I don't think we have one player that is going to replace Gatens (scoring, defense, intangibles, etc.), but with a better crop of recruits, the 3 guards coming in should be able to to more than compensate for losing Gatens and Cartwright. Cartwright's injuries and lost confidence (or whatever) has made him much easier to replace.