You are in lemon law territory now. If they can't fix the problem within 3 repairs you are entitled to a refund in most states. If you can't get some satisfaction from the subaru rep (like a new 2013), get a refund and purchase another vehicle. It will have only cost you interest paid or lost.. If you leased it, you should be able to terminate your lease without penalty.The car is still drivable but there is less travel to the clutch and it requires more force to depress. When it pops out you'll hear a loud forcefull POP, also there is a small plactic clip that'll fall from the assembly to the floor mat.
Having a part fall out repeatedly and requiring increased pedal pressure is not a normal problem. It sounds like your dealer is incapable of fixing the problem, perhaps a new dealer can advise you better.