Fulmer would have had to win 9-10 games in 2009 with top-10 recruiting classes in 2009 & expected in 2010 to keep his position. He wouldn't have kept his job with "5-6 wins a year" though that is now our new expectation, apparently.
Possibility 1: According to Fulmer's critics, he stunk and would have done worse than Kiffin in 2009. If so, he would have retired/been fired after the '09 season.
Advantages: Far less divisiveness in fan base if Fulmer failed after a one-or-done mandate following 2008 season; no Kiffin (he'd be at USC or someplace else); less perception of UT as a pariah program for undue expectations than precipitated by the mid-season firing of Fulmer following an SEC title game appearance the season before; and likely more recruits on the roster than Kiffin's brutal and bloody attrition both from his arrival and his departure.
Disadvantages: What, we don't get Kiffin for 2009?!? How would that be a bad thing? Dooley would have been as available for 2010 as he was when Kiffin bolted, and our options for HC would have been better, not worse, than they turned out to be.
Possibility 2: Fulmer bounced back with a 9-10 win season, two top-10 recruiting classes, and is looking to 2012 as his retirement.
Advantages: A good season in 2009, and well situated for good seasons in the near future, with minimal bad blood and a coming transition.
Disadvantages: How would this be a bad situation?
There's no realistic scenario in which the Kiffin debacle was a good thing or better for us, regardless of one's beliefs about Fulmer's future prospects.