Nope, you have been granted the visa
The Visa information is stored against your passport number. I would also print your grant email just for backup. If you change your passport you will need to get this sorted out.
It isn't. If you go to a state hospital and you require treatment, show them your passport and they will bill the NHS.
You shouldn't have an issue with this either as a certain amount of funds ins't a requirement. The idea of the WHV is to work to fund the trip.