The question is whether or not he deserves it.
Kubiak is an interesting case. His career record with the Texans is an uninspiring 47-49 (.490). Of course, the Texans' franchise record without Kubiak is 18-46, so by comparison Kubiak looks solid.
Compared to his peers, Kubiak's record puts him right in the middle of a grouping with Pete Carroll (.490), Jack Del Rio (.489) and Norv Turner (.486). All of those coaches have more playoff wins than Kubiak does and they don't exactly make up a murder's row of the sharpest coaches in football.
There's no perfect way to gauge how well a coach performs short of winning. We can compare the Texans' expected wins to their actual wins, but that tells us that Kubiak has been worth -0.7 wins in his time with Houston. In other words, his teams have done exactly what you'd expect them to. That's not to say he's had no impact, but he hasn't gone out and won or lost a bunch of extra games thanks to good or bad in-game decisions. He's basically the "replacement-level" version of a head coach.
His offenses in Houston have been in the 58th percentile. His defenses in the 39th percentile, though the arrival of Wade Phillips last year helped that number.
Historically, his winning percentage ranks 92nd all time. He is in the no-man's land occupied by Dave Wannstedt, Jim Mora, Mike Tice and Wayne Fontes.
McNair is in a tough position. Kubiak has done little to indicate he merits an extension. Yes, the team won a playoff game in 2011, but the division was down. His profile indicates a coach who is average at best.
However, a regime change is often a messy process and it makes no sense to endure one right when the team seems poised to go back to the playoffs. Obviously, if the Texans make the playoffs, McNair would be forced to bring Kubiak back at a hefty price tag.
If, however, the Texans falter due to injuries or bad luck, McNair will have just given an extension to a coach that he might wish he could replace.
The Texans are a talented club and I have no trouble with McNair extending Rick Smith as general manager. He's built a good roster and deserves to be rewarded. Kubiak, however, is the coaching version of "just a guy."
He's a less offensive version of Jack Del Rio.
It's almost easier to argue the Texans should just hire Phillips as head coach than it is to re-up Kubiak. Phillips fixed the defense in Houston, has a better career record by a wide margin and has taken three different teams to the playoffs. Phillips' record in Dallas was 34-22 with three playoff appearances.
McNair's hand may be forced by circumstance and it's not necessarily a mistake to give out the money to Kubiak. After all, he can always just swallow the cash should he need to part ways in the future.
Still, with the Texans so close to glory, it would be a shame to lock down a mediocre coach a moment before it is absolutely necessary.