Much like car sharing today, you'll have the option to keep the car at a remote trailhead or whatever, so it will be there in 2 hours. You'll just have to continue paying for it. Otherwise, you can end your ride and take your chances that it will still be there when you get back. In areas outside the "home" area, you'll have no choice but to keep paying since you can't "return" the car there.

People that live in cities, where this is most likely to catch on earlier, already can't leave anything in their cars unless they want to come back to a smashed window.