Indiana Jones seemingly is able to ditch class at will and travel around the world for weeks at a time without risking losing his official job as a professor. How is he able to do this? It isn't like he has some TA that will handle everything for him otherwise he wouldn't be getting mobbed by students. Does he have some sort of standing agreement with his university that allows him to take unlimited time off?
Let's pretend you're the Dean of a Univeristy, and take the example from Last Crusade, where Indie seems to run off to find his father..
If you were a world famous Historian/Archaeologist, who recovered THE ARK OF THE COVENANT...
Uncovered an ancient Thugee cult embroiled in a government conspiracy involving a child slavery ring (remember the Prime minister is at that dinner!)
As well as recovering endless artifacts and returning them to their museums, and your star professor needs time off to perform another such excursion..
Are you going to say no?
What will you gain from this, other than his resignation, and the loss of a major asset to the university?