I would guess 10 -20% will not renew if it becomes clear that Matt has not made significant coaching changes on the offensive side of the ball. It may be more than that, as a sign of protest and just lack of interest for the dollar.
To retain fan interest and ticket sales, Campbell not only needs to clean the offensive coaching house, he needs to give the fans a better explanation of his plans to right the ship. It's going to take more than his tiresome coach speak this time, I believe.
And I think he will need to do these things soonest, or risk losing recruiting / retaining players. As is, he has dug himself a pretty large hole there.