When you get a lawful court order, you comply with it. To do otherwise would result in massive fines and quite possibly executives being criminally charged. If the Apple security engineers want to quit on principle, then it truly would be on principle; there is absolutely no way Apple's legal department would allow them to ever be rehired or offered any compensation/gifts beyond a standard severance package. If engineers did quit, Apple would be forced to (at great expense) temporarily hire other people with comparable expertise in order to comply with the order.
That said, Apple security engineers probably would land on their feet.
I'm not sure Apple could be fined if its relevant employees took individual decisions that resulted in Apple's inability to comply with the court's order.
Apple doesn't have the ability to compel an individual's conduct. The court's order applies to Apple, not to named individuals. Given that, I don't see a legal basis for fines, executive criminal charges, etc.
I think there's a lot of power in the hands of a few employees (and potential replacements) here. It'll be interesting to see what they decide to do.
They could certainly be fined, charged with obstruction of justice/contempt of court etc, if Apple gave monetary or other incentives to its employees to make said decisions, as the commenter I was responding to was suggesting.
That said, Apple security engineers probably would land on their feet.