As for no entitlement during sick leave, that is a pretty obvious restriction
Yes, but the point is that the employer has in the past "removed, suspended, embargoed " the "entitlement" for a variety of reasons. Previously the "entitlement" has been restored (in most cases)
Therefore I assume using precedent the employer can remove the perk. The only difference now is that the employer forewarned the employees that the removal would be permenant.
Doesn't seem like rocket science to me.
However as you said the court case, if there is one, will decide and make a pretty penny for someone.