They are, of course, both going to wear, but the cleat is made of a softer alloy in order to wear faster than the pedal. That should mean under normal usage you should go through a number of sets of cleats before needing to replace the pedals.I also have a left cleat issue, though mine disengages at will, sod's law of course dictates at the least convenient time. is it the pedal or the cleat that wears?
left pedal illustrated below
Regarding your disengagement problem, aside from aesthetic issues, your pedal looks OK. Have you tried a new set of cleats?