Dan Mullen makes a lot of sense for many reasons. Some of them were mentioned above.
Another consideration here is the same as when Spurrier left back in 2001. Urban left a tough act to follow, just as Spurrier did. Following a legend... its almost impossible to fill those shoes. A less marque name coach might actually be more willing to take the job (and career risk) than a big name coach. Shanahan and someone else, a big name who is escaping me, declined the gators in 2001. Might see the same thing for 2010.