I had a Ford F-150 that I borrowed for a few days the black part of the key was mostly gone, I decided to drill a hole in it for a key fob.
This was not the best idea, it went into theft mode, the dashboard light blinked theft & it wasn't letting me pass no matter what.
I finally called the owner & we had to get a replacement key made on the spot, where the truck was & he had to drive 45 mins & bring title.
You gotta get a replacement key made by a mobile locksmith, approximately $250.00
As far as I know theft mode will not fail the Ford.