I thought the same thing re: Mariota making JD more likely. Again, the team has said they don't necessarily intend to install Air Raid, so I don't think that's much of influence one way or another.
Assuming this means Sam is out. From the perspective of if your #2 has to play for any serious amount of time, I much prefer SH to MM. MM maybe can mentor, but Sam can play.
Here's hoping we get something good in return if it really is the end of Howell. He's certainly a better option than any of the FAs left on the board, and cheaper, with 3 years left on his rookie deal. That alone should boost the return.
Also could be some crazy implications for the Bears and Fields.