The only recourse a traveler has is to book multiple reservations across various companies. Most major airports have at least 3-4 car rental companies, so you should be able to have several back-ups.

Does anyone know if a traveler has more recourse and/or less likelihood of this happening in the first place if they are on a pre-paid rate? In other words, if I pre-pay, should I still also book at 2-3 other companies just in case?