To kill them at the start of Chapter 11, you need a Saboteur and Synergist. Keep fighting with your remaining character, a Commando or Ravanger as you prefer, until Imperil, Deprotect and Deshell are all cast, then switch to Relentless Assault to finish it off. If those spells are all cast, you should be able to kill it before it stands up.

If it does stand up, that early in the game, I can only recommend Delta Attack, let your Sentinel take the hits while your Ravanger and Commando keep attacking.