I really don't know what Garrett has shown that should be taken as impressive.
Yes, the cumulative numbers for the 2007 offense exceeded those of 2006, but if you really analyze them, they were basically what the 2006 offense would have been had Romo started the full season. Just as a reminder, Garrett was not on the staff that season.
Romo's totals through 10.5 games in 2006 put him on pace for 4424 yards passing, along with 29 TDs and 20 INTs, for a 16 game season.
Yards per pass attempt was 8.6, which actually exceeded what he did the following season (8.1).
If this team wants to win now, which based on the Roy Williams trade it's obvious they do (giving up so much for a guy who likely would've been a free agent in the off-season)...hell, they already blew the "The Time Is Now" season THIS year. If they don't win next year, it's probably time to tear most of it down and rebuild.
Keeping Jason Garrett around, hoping he can "continue to grow" (or regress) isn't going to cut it.