I think Jason Garrett is a very, very smart cookie. He has long-standing ties to the Cowboys going back to the 90s SB years w/2 SB rings to bind him. Obviously he has a very close relationship with Jerry & feels very confident in it.
What we don't know is whether Garrett is so anxious to move up to a head coaching job that he leaves as soon as the situation he wants opens up...
OR, does he really like it in Dallas, will be patient for a little while (maybe he and Jerry already have a handshake deal in place) so he can take over as the head coach of one of the most premier football franchises in the NFL.
He's already an Asst head coach in only his 2nd year as the OC where he essentially has total control over the offense including adding the players he wants to play in the system he wants. He also now has the opportunity to study the defensive side of the ball & become familiar with those players so he'll be very conversant with the entire team when he takes over. He probably also realizes he'll have more control/influence with Jerry then he will ever have as head coach for another team whose already got a GM/owner in place that he doesn't know/might not really trust/might not be prepared to do what the necessary to put a legit SB contender on the field every year.
Also of significant importance, he's already got a lot of the pieces in place to become a SB winning offense. I also believe Romo is a big factor in Garrett's decision. He's already shown he wants to run an attacking offense which fits Romo to a tee. Romo will always look downfield for the big gain/play before he goes to the short or medium play. That allows the Cowboys to make maximum use of TO, Witten & all the other weapons--something Bledsoe couldn't do because he lacked mobility (so he couldn't buy time for his WRs to get open) combined with the fact he was an indecisive decision-maker/held on to the ball too long. Garrett is developing Romo into an elite franchise QB who more then capable of winning multiple SBs once Garrett/Jerry have the right pieces in play which include a strong running game but RBs who also good receivers out of the backfield particularly the speedy Felix Jones.
We were all very disappointed losing the playoff game to the Giants. But in reality remember our ST weren't very good, our defense wasn't as good as we hoped & our rushing game was lacking because Julius wasn't the player we needed & our OL wasn't very good in run blocking. The saying has always been that you gotta be very good in 2 out of 3 areas on your team if you want to win in the playoffs/SB & we didn't do that last year. We've added several offensive weapons in the draft & maybe 1-2 undrafted players also make the team. We didn't pick up the WR we needed but adding Felix, Bennet, Choice along with Pacman (if he reinstated) could make our offense even more prolific then last year & that's downright scary.
BTW: I'm not worried about Jason Garret leaving. I'm beginning to think Jerry & Garrett's intention is that Garrett will be the head coach of the Dallas Cowboys for many, many years.