BigMike
Unfortunate situation, hang in there.
If the pan is off or can be removed it is easier and you have more options such as welding and rethreading for OEM size but I would avoid using a helicoil due to potential leakage. It will be easier to verify that it is clean when you are through also.
I would suggest drilling/machining/resizing to use either a 9/16" or 5/8" drainplug. SAE (fine) threads are from an engineering standpoint best reserved for use in steel not aluminum.
If you want to do the repair with the pan on the car it can be done. Determine what size plug you will use if you are not using the Helicoil. With a SHARP drill bit of the correct size slowly drilll the hole making an attempt to collect all of the shavings. Then heavily coat the SHARP tap with grease and recut the threads cleaning it often and keeping grease on it to collect the chips. Be sure it is straight so the sealing washer will seat flat under the head of the plug. Flush with a couple of quarts of
oil from the top to remove any chips before you screw the plug back in place.
Good luck
Rick