This is the NFL and not the NBA or MLB.
In the past, this would indeed be the case but there have already been several in season trades in the NFL already. Trent Richardson from the Browns to the Colts, the 49ers & Chiefs swapping WR with Jonathan Baldwin & A.J. Jenkins, Jon Beason from the Panthers to the Giants have all occurred since the season started. There was also a trade of an offensive line but I can't recall who the lineman was or which teams made the deal. So yeah, you are wrong for just blatantly dismissing this possibility.
There will be no big trades for the Saints.
No one knows this for sure but this a message board where matters like this can be discussed by us fans, you know.