Here are Romo's numbers the last two years.
767 completions, 1183 attempts, 64.8 completion%, 8731 yards, 7.38 YPA, 59 TDs, 29 INTs, 93.27 QB rating.
Here are Romo's numbers for 2007 & 2009 combined.
682 completions, 1070 attempts, 63.7 completion%, 8694 yards, 8.12 YPA, 62 TDs, 28 INTs, 97.46 QB rating.
Not much difference in those numbers.
The only difference is in the wins and losses. Last two years 16-16, 2007 & 2009 24-8.
Fix the defense and the perception that Romo is on the decline will disappear.
I personally don't believe Romo is on the decline.