I don't understand, why would they fire someone who stated they intended to resign? I always thought the game was to get employees to volunteer to leave instead of formally terminating them?
"Senior engineering lead resigns in protest of corporate directive", on the other hand, seems like a call to arms for the conscience-driven; a thorn in corporate's side. Better to squash it and deal with the one-off "firing". Especially if it's for "cause"—then they can give nothing as severance, and quote a violation of the "employee agreement" as the reason.