I drove from St. Louis yesterday morning and got home (~230 miles) with only about 5 miles range showing. I was already late for a sword fighting event a few miles away, but I plugged in while I was changing clothes and getting ready. I had 10 miles range showing when I left the house. My destination is an easy (rural roads) 3-4 miles away, and the battery still showed 7-8 miles when I got there, which should've been plenty to get me home. But, for some reason, I decided to leave the key fob in the cup holder in the car, something I normally never do. Apparently, that is enough to keep the car from sleeping and makes it think I'm about to get in and drive which increases the "vampire drain" on the battery. In this case it was enough to take it to zero.
Well, I got news for you. This isn't entirely your fault. Your MS absolutely should have retained that range while while you were at your event. My car sleeps just fine even with the fob inside the car. It DOES NOT measurably increase vampire drain in my experience. I probably would've done the same thing knowing that 7-8 miles was more than enough to get home.