If Ezreal kills Lucian with his defender trigger before Lucian's attacker trigger resolves, does Lucian still deal damage?

Ruling: No, Lucian does not deal damage. If Lucian dies to Ezreal's trigger before his own trigger resolves, the returned value would be Null and wouldn't do any damage.

Sequence:

• Ezreal's defender ability triggers first
• Ezreal deals 3 damage to Lucian, killing him
• Lucian's attacker trigger attempts to resolve
• Since Lucian is no longer in play (in trash), the ability executes what it can but cannot deal damage

Nuances:

• The trigger doesn't completely disappear, but it returns a Null value since the source is no longer present
• The ability executes what it can, but cannot deal damage when the source unit is in the trash