His story is not written yet, but it's not looking good.
Qualitative:
He has definitely improved, plays hard, and is unselfish - a good fit for Billup's system. He also can play multiple positions, and rebounds well. But, right now, he just doesn't put enough pressure on the opponents. If he continues to improve, he might become a Steve Blake-level player. We'll see.
Quantitative:
He's shooting 30.4 3fg% this year (career 26.7%) - that's not going to cut it. Frankly NBA average (35 %) is still not good enough when combined with his other abilities. If he can get up to 37 3fg%, he's better better than a "replacement player". Right now, he's definitely not. It's not obvious he's going to get there.
Comp:
Let's compare him to Aminu. Aminu shot 33.2 3fg% for his career, and he was left WIDE open. Discounting shooting, Aminu brought a lot more to the table that CJE does. Aminu's played 41 games in the last 3 years. Idk if he's injured, or if the NBA has given up on him.