As is discussed above, it's happened at OU in football, with our (admittedly much-criticized) backup QB.
As long as OU is good, we won't mind, as we wouldn't likely lose a top-drawer player. If Spangler, say, had another year of eligibility this year, is it likely he would want to transfer? No. What would he gain?
On the other hand, if a player of, say, DJ Bennett's caliber had gotten his degree and wanted to spend his final year of eligibility elsewhere so that he might see more playing time, I don't think anyone would have been upset. Sorry to see him go? Sure, but it wouldn't have been a big hit to the team and I think most fans would have understood DJ wanting to get as much playing time as possible in his final season.