I don't think the score will have any effect on how long the starters stay in the game. I would think the coaching staff is looking for the starters to get a certain number of snaps, and for all the backups - specifically the guys on the bubble to make the roster - get a certain number of snaps.
I would think the starters would be out there for about twenty to thirty plays regardless of if that's early in the second quarter or well into the third.
But yeah, the line will have its hands full keeping Suh away from Brady. As I recall from last year Detroit was able to get a lot of pressure early, then the Pats made some adjustments, bringing Crumpler across to help protect in the middle of the line. Once they did that Brady had more time and what was a close game turned into a relatively easy win.