It is indeed hard to foresee attrition, but that's the whole point: It always is.
If you look back, several of our transfers would've seemed preposterous a year beforehand: Horford, Smotrycz, Brundidge, Dawkins, Doyle. With each individual player, the chances always appear low, but if you pool those odds, they rise to the point that you almost expect a departure.
As such, it would be logical for U-M to keep on recruiting the big fish regardless of whether we have an open scholarship. Things happen.