It's not Ainge's job to see the future. He has to decide now what contract he will offer Rondo in the offseason (assuming he doesn't get hit by a bus or something) and if he thinks Rondo will accept. If not, he should try to trade him for a legitimate asset.
Personally I would offer rondo 60-65 million over 4 years. I don't think Rondo would accept, but it doesn't look like his trade market exists right now. So he'll probably go to free agency and I would make him my offer.
A little bit off topic now, but who here would rather have Isaiah Thomas at 4 yrs/27M than Rondo at 4/65M? (raises hand)
Also apologize for going off topic
Not to sound like a hater but I don see any team winning a chip with I.T. has their starting point Guard. YES I seen the video about his efficiency compared to Kyrie's and how he outplays him (so to speak)... Only thing is IT never played against a team where he was a main focal point of another teams defense.
I also believe at his size, any zone will mask his defensive deficiencies at the same time make his front court seem as their defense isn't as good as it really is because their going to be playing a ton of help D. He's best as a 6th man IMO. Put him against Shaun Livingston (6ft.6"). No way that man guards him and Shawn's a 2nd unit player himself