If he continues his current level of play through the rest of this season and next year, he's going to get $20 million per year or more.
AB is going to be the really tough decision for Ainge and crew, I think. He's improved so much while on the team, and he's the longest tenured Celt. But his injury history is not insignificant, and his size and reliance on lateral quickness means aging will be a concern.
On top of that, AB was an average starting shooting guard a year or so ago. He's clearly better than that now, but I would wonder how long he can sustain that sort of production.