As a rule if the document is silent then all plans have a provision in them that say the Administrator has the authority to reasonably interpret the plan provisions as long as doing so is non-discriminatory and reasonable.
I think either date can have a case is made meets those criteria. But to me LOA doesn't mean terminated so the more natural or dictionary meaning of the word employed says a person on a LOA is employed. As such that points towards the 7/1 date,.