Critically injured Orks may survive to fight again after an extensive rebuild at the Mad Dok's. An Ork with a Cybork body can survive terrible injuries and so gains a 5+ invulnerable saving throw.
Errata — Chapter Approved: Codex: Orks Q&A (v1.0): Because this is an Invulnerable save, a Cybork body is ignored entirely for Mixed Armour purposes — that rule only concerns Armour saves.