I think the season would have to end very badly for Kyrie to consider going elsewhere.
If you asked me before the season began I would've had zero doubt that Irving would re-sign. During the last months I've seen a Kyrie who has been fully committed to the mission of the Celtics.
He tries to share the ball to make everybody comfortable, which led to him being too unselfish at the start with bad results as the young guys weren't able to step up to being primary scorers. After that he played more to his own style, but also played hard on defense every night. Leading by example. However we've seen that others unfortunately didn't follow the example he set.
I believe that Kyrie is pointing this out by his remark that he should be a better leader and that players don't understand what it takes to go to the NBA Finals. He also has questioned the shot selection and mentality of his teammates, because he's severely disappointed how the season is going so far. Considering that (kind of) fall out to coach Stevens in Orlando I'm also convinced that Kyrie isn't happy with the leadership or lack thereof. In his view players need to be held accountable and that at this moment he's the only one able to carry the team.
Kyrie understands the importance of home court advantage and is keen on getting that #1 seed. He only has one thing on his mind: trying to win a championship. I don't think Kyrie will make a rash decision, but a first round exit and chemistry issues with the staff and teammates may change his mind on committing the rest of his prime to Boston.
So I have become a little worried. I don't think we can win a championship without Irving in the short term. By the way, I'm fully on Irving's side. His latest commentary isn't making the situation better, but a lot has happened and we don't know what has been said during those team meetings. In Irving I see one of the few players on the Celtics that has been playing with the right attitude consistently.