Does Deathknell trigger happen after a unit heals on a battlefield?

Yes, Deathknell triggers resolve after units are healed following a combat showdown.

According to the official rules and RiftJudge FAQs (specifically FAQs #10061, #9786, and #9514), the sequence during the Combat Cleanup phase ensures that units are healed before Deathknell abilities resolve.

The Official Combat Cleanup Sequence

1. Combat Damage Step: Combat damage is assigned and dealt to units (Rule 460.2).
2. Triggering Deathknell: Units with lethal damage trigger their Deathknell abilities. These triggers are added to the chain as Pending Items (Rule 808.1.d.2, Rule 323.4).
3. Killing Units: Units with lethal damage are moved to the trash (Rule 323.5).
4. Healing: All surviving units on the battlefield are healed (Rule 461.1.a.1).
5. Resolution: The game returns to the FEPR (Finalize, Execute, Pass, Resolve) process. The Deathknell triggers that were added to the chain in Step 2 are now finalized and resolved (Rule 808.1.d.3).

Key Consequences

• Healing First: Because healing occurs in Step 4, any non-lethal damage on surviving units is cleared before your Deathknell effects resolve.
• No "Saving" Units: Because units with lethal damage are moved to the trash in Step 3, Deathknell effects cannot be used to "save" a unit that took lethal combat damage.
• No "Finishing Off": Because healing occurs before the Deathknell triggers resolve in Step 5, you cannot use Deathknell effects to finish off enemy units that survived the combat damage, as they will be healed to full health before the effect resolves.