Matheson's pretty comfortable in his House seat. He'd be foolish to give it up for a longshot at taking down Herbert. Trailing by 10% this far out isn't horrible...for a little-known challenger. Thing is, Matheson is already pretty well-known, so making up that deficit would be quite a challenge for him.
In his house seat as it is currently crafted, you mean? 
Of course they'll probably try to get rid of him again, but I find it unlikely that they could give him a raw enough deal that he would actually be better off attempting an uphill battle against the incumbent Governor.
