1) It's already came out of Westbrook's camp that there's absolutely no way he's signing an extension with the Warriors, and it can be expected that goes the same for any extend-and-trade scenario.
https://twitter.com/daldridgetnt/status/7500924056263802882) Essentially, this forces OKC's hand to trade him. They absolutely cannot let this happen again, especially fresh off the KD situation. They're going to open up a market for him and get as much as they can for him. Further, they have no interest in waiting until the trade deadline to do so. That only lessens his value and wins them unnecessary games that they will want to avoid for a better draft pick next summer.
3) The Lakers situation has changed. Beforehand, they had all of this open space, and it was thought that they would do a Celtics situation and be patient for one more year utilizing one and two year contracts to have maximum cap space in 2017. However, they went out and signed a ton of money in multiyear contracts in average free agents in Mozgov, Deng, and Clarkson, so they no longer have space for two max contracts next year. To get him, LA is going to have to trade both Ingram and Russell, so that would leave Westbrook with Clarkson, Deng, Mozgov, and Randle as the primary components of that team moving forward with space to take another big free agent. So, yeah, if Westbrook wants to be in a winning situation, then the Lakers aren't necessarily going to be that, so they're definitely not nearly the threat that they once were to sign him next summer.
We'd really have to talk to his guys to see where his head is at regarding next summer. I doubt that he will give anyone even a "handshake agreement" that he'll re-sign with them, but it might not require that much to take that chance. You'd have his Bird Rights and be able to sign him to the most money for the longest. So if you'd ask him if Boston would be a place that he could see himself long-term on a max contract in a winning situation and he said yes, then that might be enough to take a chance on someone as talented as Westbrook.
Though I certainly understand the uneasiness of the whole situation and not wanting to take that chance, but people are being ridiculously picky if you don't want him because he's not exactly fitting your style or something. He's an MVP-level talent, and every team should want a talent like Westbrook, especially a team that is seemingly perfectly built with defensive 3 and D guys surrounding him.