If they accepted their positions back and aren't actively looking for work elsewhere, then these people are idiots.
You don't "accidentally" let go of an entire department, then weeks later rehired them all back. This should tell all Tesla employees how valuable they are to the company... and how badly the company is managed.
Elon Musk's recent cost-cutting move to fire almost all of Tesla's Supercharger team was met with confusion and more than a little panic. Now, he seems to have started rehiring the same team, although just how many have returned is unclear. The Supercharger network has been key to Tesla's success, and will likely continue to be as competition in the EV space heats up.