"I have seen plenty of trees in the local area showing these signs."
I wouldn't jump to any conclusions.  The symptoms shown on the leaves in your photo's could just as likely be caused by Verticilliam Wilt which which is quite common and not necessarily fatal if treated.  I've had this in the orchard I planted in 2008.  It's a soil born fungal disease which blocks the xylem which carries water and nutrients up from the roots to the rest of the plant (not just in olives).  If you cut through a branch just below the affected area, you'll usually see brown staining.