This looks all but final.
From the Daily (link):
The University’s Board of Regents will conduct a special meeting tomorrow morning regarding a proposal to bring the 2013 NHL Winter Classic to Ann Arbor, according to a press release.
The meeting, held at 10 a.m. at the Fleming Administration Building, will feature a discussion about “authorization to enter into a facility-use lease for the NHL Winter Classic.”
TSN's Bob McKenzie also just tweeted this:
"Just a reminder, 2013 NHL Winter Classic (TOR vs. DET at U of Michigan Big House) will be made official at Thursday news conference(s)."