If Yasuo attacks a battlefield and his attack trigger goes off but dies to a hidden blade before combat completes, does the defending unit on the battlefield still heal?

Ruling: Yes, the unit on the battlefield still heals. Once Yasuo's attack trigger goes off, combat has started (he was designated an attacker), and even if Yasuo dies, combat continues through all remaining steps including the Resolution step where damage is healed.

Sequence:

• Yasuo applies contested to enemy battlefield (combat starts)
• Yasuo's attack trigger goes off
• Yasuo dies to hidden blade
• Combat continues through Showdown step
• Combat continues through Damage step
• Resolution step occurs where damage is healed

Nuances:

• Combat officially starts when a unit applies contested to a battlefield controlled by an enemy
• There is also "surprise defence" which occurs when a unit shows up to a battlefield an opponent has applied contested to but no one controls