twice. what happens is that the ICE shuts down and the dashboard display reads "stop safely now." at this point the system has shut down. then when you stop, you can restart it, but the ICE will shut down immediately - though the system will be active and you will be able to drive on electric power for as long as the battery is able. you'll be at 25-30mph until the battery gets low and then your speed will gradually slow to a crawl until you have no more power.

what happens then (at least is my case) is you ring roadside assistance and they dispatch a service vehicle to deliver 2 gallons. the network is very complete, as both times i was in the middle of nowhere and the service vehicles were dispatched from the very next town (even though in one case, calling it a "town" would be a stretch...more like a desert outpost).