I can tell you from personal experience that if the person you loaned your vehicle to gets into an accident the least of your worries is if your insurance or his/her insurance covers you. In the end the attorneys will come after the owner regardless...very few people carry anymore than state required liability limits and even fewer will use $500,000 limits. Personal injury can quickly exceed $500,000. Attorney's will come after you for anything above your limit amounts.
Its one of the reasons I stopped carrying vehicle specific insurance. I rely on an umbrella policy that covers far more (multi millions) and significantly less cost.