You can't treat the athletes differently than you treat normal students or contracted employees.
The flaw in this idea is taking everything back because of not completing a small portion of the agreement, when a large portion was already earned.
Example, if a student uses federal financial aid the expectation is for them to go to school (since they've received cash) but if they withdraw there is a fork in the road that determines what happens. If they've completed 60% or more of the term/payment period nothing happens, they keep the money. If they withdraw before the 60% mark then funds have to be returned, but not ALL of it..the amount returned is prorated based on what's "already been earned".
Likewise some hospitals have nurses/doctors sign contracts to stay with the hospital for a certain period. If they leave before that contract is up, there is a penalty but it's not returning all money they made while there.
Also coaches sign contracts and leave before it's up but don't return the entire amount of money earned for work already performed. There are buyouts which are usually prorated so that the more of the contract was fulfilled, the less the buyout is.
So like I said before when a similar idea was brought up about canceling or withholding something that has already been earned...great idea, just apply it to the rest of our society first before applying it to only college student-athletes.
Now if they had to pay back a prorated portion, that's at least worth discussing. Question one, is would the probation period be based on the academic year or the start and end of the year for the sport in question?