When Volibear and Kayn fight and Kayn triggers his ability to not take damage, what happens to the showdown if neither unit dies?

Ruling: At the end of combat, if units from both sides remain, the attacker's units are recalled to base.

Sequence:

• Combat occurs between Volibear and Kayn
• Kayn triggers his ability and does not take damage
• Neither unit kills the other
• At end of combat, attacker's units are recalled to base