When Sara "Dippity" is in critical mode and has additional armor on the final limb when it is blown off, the Extra Life ability is triggered which means instead of ending the game the player will only discard all of the armor upgrades back to base armor. If the action card Commabackk is played it would not draw any cards because Sara "Dippity" does not have less limbs than earlier in the turn.
Yes. Any active pilot with a critical bonus will activate the moment their robot goes into critical mode (Critical Mode is when a robot only has one limb remaining). In critical, if a limb is regenrated, the pilot will go out of critical mode and then the Critical Bonus could be retriggered if they go back into Critical Mode. This could happen many times during one game.