Would you be worried about the Cowboys clinching the first round bye early? I have Dez and will be needing him weeks 15 & 16. In our league you can still trade up until Monday.
This is just my believe, but I don't think they rest guys in Week 15.
Week 16 they maybe get less work or snaps but I still think they will be worth putting in lineups.
Week 17 probably a different story. I would think they make them prepare, play a series or two and then pull them - like a preseason game. Because of the bye they likely clinch if they haven't already, I can't see them giving guys what would be about a month off, which makes me think their guys will be fantasy usable Weeks 15 and 16. Like I said, that's just my feelings on it.
