If my unit with Assault is dealt damage by Ruined Rex's Deathknell, will I score before the unit dies from losing its Assault bonus?

Ruling: Yes, you will score before your unit loses its Assault bonus and dies. The attacker designation (and thus the Assault bonus) is not removed until combat ends as the very last step, which occurs after determining the combat result and establishing control.

Sequence:

• Combat damage is dealt and Ruined Rex is killed
• Ruined Rex's Deathknell resolves via FEPR, dealing damage to your unit (which still has Assault active)
• Combat result is determined - your unit survived, so you win
• Control is established and you score from Conquer
• Combat ends and attacker designation is removed (Rule 461.7.a)
• Only now does your unit lose Assault; if the marked damage is now lethal, the unit dies

Nuances:

• The Assault bonus remains active throughout result determination and scoring because the attacker designation persists until Rule 461.7.a executes
• Death from losing the Assault bonus occurs after scoring is complete