if the Celtics get the number one pick, they will not trade it for George or Butler IMO. They will instead groom Fultz and that may make IT expendable, as crazy as it sounds.
If a trade for George or Butler is on the table for the first overall pick, I think the Celtics will do the trade.
IT is 28 years old, two time all star, and averages nearly 30ppg this season.
Bradley is a similar age and playing elite defense with good offense.
Horford is around 30 years old and still a reliable option.
They usually have two decent forwards, however they don't have an all star at one of those positions. Butler or George would be an upgrade over one of them. It would also keep them in win mode and potentially give them a better chance at title contention. Also, that core would all be in their prime years together.
Now I can see why a team might want to draft Fultz and have him succeed IT, but in that scenario they would need to be confident they could make their upgrades via other means. For instance persuading Hayward to join them, or Blake Griffin. That could be an appealing option since they'd get IT's successor and an all star, but it's risky business to bet on one of the big names signing for them and shunning their existing team. Plus, there would have to be a belief that Fultz can be special, maybe he will, but we've seen countless players down the years never live up to the hype. If he's one of them, they'll spend a long time going "what if" we had traded for Butler or George, maybe we would have another banner in the rafters. The flip could also happen if they don't win with Butler or George, but Fultz is a key member on a title team elsewhere, they'll be wishing they would have drafted him.
For me, I see them trading the pick for a current all star and placing their eggs in that basket.