Yes they will still work for the person that each MB was assigned to in your MDE account(s). The batteries are dead so you can't use them for long range RF features such as additional attraction interactions or automatic Attraction picture. All other functions will work just fine since these additional features don't required a battery.
Yes and you will want to update your PIN assigned on your MDE account. You can do that today if you plan to reuse your default Credit card for your room charges once you arrive at the resort. Then you are all set.