Can you play Shen (or other reaction units) to a battlefield in response to a deathknell trigger that resulted from combat damage?

Ruling: This creates an illegal game state under current rules (version 1.1). Until the rules update (version 1.2), this is at head judge discretion. At the Houston tournament, the ruling is that it starts another combat with the same attacker/defender roles.

Sequence: (Under Houston ruling)

• Combat damage occurs, units die (deathknell triggers)
• Units heal
• Attackers recall
• Players/units lose attacker/defender status
• Deathknell is finalized on the chain
• In response to deathknell, play Shen before contested is cleared
• Resolve Shen
• If there's no clear winner, attackers recall before second combat
• Start a new full combat/showdown with same attacker/defender roles

Nuances:

• The easiest way to avoid this rules issue is to play the reaction unit before the combat damage assignment step
• Different judges may rule differently: some say it's illegal, some say attacker recalls, some say you don't control the battlefield anymore
• This interaction is unintended and will be fixed in rules version 1.2
• Zhonya's (a gear) doesn't create the same illegal state issue since it goes back to base
• The illegal state occurs because attackers have already recalled but contested status hasn't cleared yet, leading to multiple players potentially gaining control of the battlefield