I am joining this thread a bit late and, admittedly, haven't read all the posts.
That said, the window is as open as the Cowboys want it to be. I know, a bit cryptic. Most, but not everyone, would argue you build a team from the inside out with a focus on the trenches. I recognize that many would argue for the franchise QB first. For me it is a bit of which came first, chicken or egg?
Regardless, we have a great offensive line that is, contractually, locked in for several years. We also have a good, not great DL, that is trending up. Disregarding, for a moment, the other pieces of the team and the whole debate about whether Dak is or is not a franchise QB, I would argue that Dak or someone of similar capabilities could and should keep our window of opportunity open for a SB run.
Not to beat a dead horse but, if you acknowledge that the Cowboys have adequate talent to reach the SB, then the biggest potential drawback is coaching.
I am not a fan of Garrett and have offered that, more often than not, he has under-performed given the talent level. That said, Garrett may be one of the few that can put up with the circus called the Dallas Cowboys.
So, the window is open and, in my opinion, will stay open for quite some time. Nonetheless, pulling the Cowboys through the window requires a change in coaching.