When a defending unit survives at the battlefield where it was attacked and the attacker is still alive, what happens?

According to the Riftbound core rules and the established FAQs, if both the attacking and defending units remain at a battlefield after the combat damage step, the attacking units are recalled to their base.

According to Rule 461.1.a.2 and FAQ 5531:

• Combat Resolution: After damage is dealt, if both players still have surviving units at the battlefield, the attacking units are recalled to base.
• Control: The defender retains control of the battlefield, as the attackers have been recalled and no conquest has occurred.
• Recall Nuance: Per FAQ 6909, this recall does not count as a "move," so move-related triggers will not fire. Additionally, units recalled in this manner remain exhausted if they were exhausted when they entered the showdown.

In summary, the attacker is forced to retreat to their base, and the defender maintains their position and control of the battlefield.