1. Neither of these really apply. I don't need to assign this to another vehicle, so I could care less about that (true, my title for this thread says "transferable" so it's a bit misleading). I don't really want to cancel it either. To me, cancellation says you signed up for it, then decided later that you didn't want it, and want a refund. But neither of these covers the condition of what happens if a car gets totaled and you can't possibly get it serviced anymore. It's a situation that isn't explicitly covered in the document, and in arbitration I would think there's at least a leg to stand on there. Surprised it's not explicitly covered in the service agreement, in fact.
2. No, I don't read everything I sign, and likely neither do you. I bet nobody reads everything they sign. Did you know that the Apple iTunes End User Agreement is 56 pages? Did you read it all before clicking the checkbox? If by some miracle you did, did you understand everything you read? Doubt it. If so, you're either a lawyer or a liar (perhaps not mutually exclusive).
3. Lots of Tesla's policies change. In fact, the service agreement even says that anything in the agreement can be changed with Tesla approval.
Regardless of what the document says, giving a partial refund for the unused portion of the plan in this circumstance is basic decency. Not doing so makes customers upset.