I haven't seen all the practices, so I am only partially informed. But the hunch is that even if he were cleared medically he wouldn't be in game shape enough to help us.
As Gailey alluded to, his leadership would help if he could just help with 15-20 snaps.
It is apparent that something is of more serious concern medically or he would have been cleared. Football is insignificant as we all know when one deals with something like a kidney.
Here's praying for Gathers to have a long and healthy life irregardless of football.