If you want them (or anyone) to remain as employees, you ought to treat them nicely. If all of ARM's cleaning staff walked out, the management could probably find replacements and save a few pennies into the bargain. If all their chip designers walk out, they don't have a company anymore. They're fucked, with the proverbial wrought iron fence wrapped in curare tipped barbed wire.
(With due apologies to cleaning staff, but they are probably already aware of this. On the other hand, I don't think anyone believes that this is the 15% of the workforce that ARM's management have in their sights.)