They don't. They're much better at estimating their future fuel usage and routing/scheduling a refill. That refill will probably be at some kind of base station

They don't. They're much better at estimating their future fuel usage and routing/scheduling a refill. That refill will probably be at some kind of base station for a while, yes, but you'd probably want to run the car through a tiny maintenance cycle every 12 hours anyway, so that works out. If they somehow actually run out of gas, they do exactly the same thing you would: call family or a friend (AKA home base) and they'll drive a can out to you, or they call AAA, who does the same.