^ Players do not have an out when coaches leave. One of the many criticisms of the NCAA. Their release is up to the school and often conditional on them attending certain schools (different conference being the most common).
But while Arizona may eventually end up facing sanctions for improper benefits, we are only seeing hearings associated with the FBI investigation at this point. The NCAA will then have to conduct their own investigation (with significantly less power than the FBI), hold their own hearings, and hand down a decision. If Green is planning to be one and done, it's not out of the question that he is out of Arizona by the time sanctions are actually in force.
The NCAA has no desire at all to see this happen quickly. There is enormous risk to their credibility as an institution, not that they have much to start with. But there are almost no major programs who haven't already had their names raised in this. And if it's happening in basketball, it's happening in football. If they penalise everyone who has broken the rules, the NCAA will probably bankrupt themselves in the process (no one is watching an NCAA tournament without Duke, Carolina, Kentucky, Kansas, Michigan State, UCLA, Arizona, etc). So they have every incentive to be unable to gather the requisite evidence.