re: How far would Alabama/LSU fall if they lost Saban/Miles in April

Big loss, but all depends on the next hire. In many cases, the program fell apart (or in some cases, the big name coach left the program weaker than first thought). But some programs have maintained across several coaching changes. Miami was quite successful even though they moved through several coaches in their run of dominance. LSU, as mentioned above, hasn't seem to have lost their luster. So it can be done, but it's all in who comes next. There's no such thing as a program that runs itself.