Here's what I think....I'm sure your day will be better now.
If I'm Meyer, I'd have Mullen there for as many practices as possible...remember recruiting dead period is from like Dec. 22 to Jan. 4 or thereabouts, so Mullen can't contact recruits anyway. I think they can call him, but he can't make contact. I'd have Mullen there as much as possible TO HELP TRAIN my new OC. Looks like they will move the WR coach over to OC. During the game, I'd have both of them sitting side by side in the booth with Mullen calling the game. If this were a regular bowl game with no implications, I'd let my new guy call the plays with Mullen's assistance. But for all the marbles, I'd go with the guy who helped the most in getting me there.
I don't have a problem with him going back and doing this. I think he can milk it for all it's worth by telling Bumphis to watch Harvin and say this is where you'll be in my offense and telling Patterson to watch so and so and draw up some plays with Russell next week and say watch when we run this in the game, etc. Then when Fla. beats the crap out of them, that will only help us as well. Not to mention the PR from Mullen getting mentioned on national TV that he is coaching his last game and will be moving to Miss. State.
I don't see a negative in him going. People have compared this to Croom's first class. We had like 2 commitments when Croom was hired and he didn't come to mid January. It's not like that this time.