I definitely don't think Chip will go anywhere. He have transformed Philly into a contender within two year's time and it's much shorter than what it took Garrett to revamp Dallas Cowboys. I'm interested to see the new changes years to come.
Chip took over from Andy Reid... one of the better head coaches in the league.
Garrett took over from Wade Phillips... one of the better defensive coordinators in the NFL... but also one of the worst head coaches in the NFL.
Reid had some good players and he had already instilled discipline and had run one of the better teams for the past decade. Yeah, the team got tired of Andy and he eventually lost the team but it was a franchise that had been run well for the most part. The right culture was, for the most part, intact when Kelly got to Philly. He had to implement his offense and find a decent defensive coordinator, but there simply wasn't that much to "fix" in that team.
Philly's salary cap was in pretty good shape and they could spend to bring in the free agents Kelly wanted. Also, the unusual nature of Chip's offensive scheme gave him an advantage going in too. The NFL has now had not quite two years to see what Kelly does on offense and they will continue to slow it down better than they have to this point. Plus, unlike Garrett, Kelly had a good bit of head coaching experience coming in, even if it wasn't in the NFL.
On the other hand, when Garrett took over from Wade Phillips, not only was he taking over from a coach that was very soft (both literally and figuratively) but he was inheriting a franchise that had been dysfunctional for the better part of fifteen years. Discipline was non existent with Wade as HC and the team hadn't been pushed since Parcells left in 2006. Garrett needed to get rid of many high priced, low producing veterans who didn't seem to care that much about wins and losses and had long ago waved goodbye to their primes. He needed to change the way the team drafted, the way they analyzed talent, the way they ran free agency, as well as how they practiced and how they churned the roster. Garrett pretty much had to start from scratch. He had to root out the wrong attitude, work ethic, and age from the roster. All with a salary cap that was screwed before he ever took the HC position in Dallas.
I'm not saying that Chip Kelly isn't a good coach, because I think he is. Really good. I'm not saying that Garrett is a better coach than Kelly is either, because I'm not sure which is better at this point.
All I'm saying is that the job Garrett had in Dallas was a much larger scale endeavor than what Kelly inherited in the city of brotherly love.