Interesting article on why the Iraqi Air Force didn’t fight in 2003:
Rather than being afraid to fight in 2003 as the Americans initially speculated, Iraq was simply following the same pattern it had set nearly twenty years before. Ever since the Iran-Iraq War, Baghdad had tried to protect its air force from its enemies by hiding them, either within the country, or in neighboring states during conflicts. Because Saddam did not see the U.S.-led coalition in 2003 as a real threat to his power, he did not want to waste his planes during the invasion, and chose to bury and camouflage them instead. That was the real lesson from the episode, in that it revealed Saddam’s flawed perceptions of the war that would unseat him.
I suspect that this may be framed a bit too strongly. Saddam doesn’t need to have believed that the Coalition would leave him in power, just that the there was a chance that he would remain in (or return to) power combined with a (probably correct) belief that the air force would have been quickly destroyed to no good effect if it had fought. In this case, it makes sense to save the air force even if Saddam thought that he would probably be deposed.
Whether MiG-25s could actually be returned to service after being buried in the desert is another question altogether.