If Mitt wins both Arizona and Michigan, Super Tuesday will be much more tilted towards him and the race will be over. It's possible that Santorum will win here and there, but like Florida in '08, Michigan is the last chance for someone to completely unseat the frontrunner.
The last polls are heading Mitt's way. Today's Rasmussen from Michigan is Romney 40, Santorum 34, Paul 10, Gingrich 9 while Mitchell/Rosetta Stone shows him at Romney 36, Santorum 33, Paul 12, Gingrich 9. Arizona will not be close and Rasmussen confirms with Romney 42, Santorum 29, Gingrich 16, Paul 8.
Add that to the reality that many people have already voted in both Michigan and AZ, and Romney leads by 23% and 30% respectively among that subset, I doubt any amount of Democrats voting in our primaries can swing it to Rick. The last debate has helped many conservatives realize that Rick Santorum, "I was against it, before I voted for it," is not a Reaganesque savior. And sorry, but Newt is done.