I think Westbrook signing a new deal make sense for two reasons:
1. If he wants to be the guy on a team, then there is no better opportunity than sticking with OKC because they are a well run team and they will build around him. This contract extension gives them time to make moves to build a strong supporting cast for him. Any additions will likely be players that Westbrook wants on his team, or at least they will fit the way they are likely to play with Westbrook as the main man. So by signing the extension it allows them to focus on outside free agents next year, rather than having to balance re-signing Westbrook, re-signing their other free agents, and attracting outside free agents.
2a. It gives Westbrook flexibility if things go wrong. In an ideal world they will manage to attract at least one big name player to come and join them next year. However, the Mavericks are a perfect example of a team that each year seems to go after big name free agents and get shunned. If that happens to OKC, which is possible, then by giving them a chance it doesn't really make Westbrook look bad if he decides to leave because he's at least given them a chance to build around him.
2b. It gives Westbrook flexibility if things go right. It is likely their plan will be to target the addition of at least one big name free agent next year. So let's say they manage to attract Blake Griffin (28 in 2017) or Gordon Hayward (27 in 2017); re-sign Steven Adams (24 in 2017), and perhaps one or both of Andre Roberson (26 in 2017) and Victor Oladipo (25 in 2017); and fill the rest of their roster with good supporting players. At this point they would be a strong contender in the 2017/18 season and beyond. Fast forward to 2018 when Westbrook is likely to opt out, it is likely he would re-sign with OKC because they would have a strong starting line up and rotation that would mostly be in their prime years together.
2c. It gives OKC flexibility to see what a Westbrook led OKC team can do. If they do well, Westbrook signs a new deal. If they have a lacklustre 2016/17 season and/or fail to attract outside free agents in 2017, then they have at least given it a shot and can trade Westbrook this time next year for whatever they can get.
For me, I think this deal makes sense for both parties and hopefully Westbrook stays in OKC for his entire career. I like one team players and hopefully he is one of them. Like I said above, this gives him the best chance to be the guy on a well run team. Sure Durant left, but I suspect that was more down to Durant than OKC (unless of course you argue they should have kept Durant and got rid of Westbrook, if that was a possibility to at all?). So overall it gives both parties time to see what happens, and the flexibility to go their separate ways if things go awry.
