Since the 1980-81 season, there have been a total of 34 Super Bowls played, elite QB's have won 21 of them...
These are the QB's drafted since Joe Montana that would be considered in the same class as Romo... (The number represents how many Super Bowls they won)
Montana 4
Moon
Marino
Elway 2
Kelly
Aikman 3
Favre 1
P. Manning 1
Brady 4
Warner 1
Brees 1
Rivers
Roethlisberger 2
Rodgers 1
Ryan
Wilson 1
Luck (maybe?)
Yes, lesser QB's have won their share...
Jim Plunkett 2
Joe Theismann 1
Jim McMahon 1
Phil Simms 1
Jeff Hostetler 1
Doug Williams 1
Mark Rypien 1
Trent Dilfer 1
Brad Johnson 1
Eli Manning 2
Joe Flacco 1
So it's definitely possible to win without an elite QB, but the odds are at least 2/1 every year in favor of the teams with elite QB's... We see that it's possible to sneak up and win one title on the back of a great defense, but if you want to win two or more Super Bowls in a decade, then it becomes almost mandatory that you have an elite QB...
When you have a QB as elite as Tony Romo, you don't need to start worrying about what will happen 3 years from now... You already have that elusive HOF caliber QB, and your team is already pretty decent overall, NOW is the time to win, now is the time to go for broke... The majority of QB's who are as good as Romo win championships, and he's so due for some playoff success, I don't see any reason why we shouldn't expect that Romo will finish his career like John Elway...
Romo will still be starting at QB for Dallas in the 2018 season... Finally winning the Super Bowl will keep him coming back... When Romo finally does hang it up, if you haven't found an elite QB to step in, then it's time to use high draft picks to improve your chances of finding one...