I don't think it matters who the running back is, production in the running game will be down. Teams understand that the Cowboys are a running team now, and will gameplan early and often accordingly. Don't forget the monster days that Murray had to begin the season against teams like St. Louis, TN, etc. Doesn't matter who is playing - just by matter of focus, you will see the running game as less productive.
I expect you will see an increase in volume passing stats. Because teams will load the box a bit more, expect us to see a slight increase in pass attempts. Romo was highly efficient this year, but his overall yardage was down (although his Avg/attempt was up). He was also injured through several games and that affected his throwing. After understanding how to manage his back better, I think you can expect a bit more health through some games (the injury he got in Washington was uncommon).
For the offense as a whole, it's hard to tell. I think the offense will go for a third straight year of dominance - this year they were good in everything you have to be good in - they stayed ahead of the chains, they were BOMB on third down, and they scored in the redzone. You may see a tick up in passing and down in running just because of how defenses will play, but as a whole the unit should continue to dominate.
