If a stunned attacking unit has more might, does the attacker or defender bounce?

In this situation, the attacking unit bounces back to its base.

According to RiftJudge FAQ #4142 and RiftJudge FAQ #2162, when combat concludes, if any defending units remain on the battlefield, the attacking units are recalled to their base. This applies regardless of might values and even if the attacker has higher might than the defender.

Furthermore, Rule 423.1.b and FAQ #9712 specify that a stunned unit does not contribute its might to damage in the combat damage step. Therefore, even if the attacker has higher base might, its contribution to the combat damage is zero while stunned, making it impossible for the attacker to eliminate the defender in that combat. Since the defender survives, the attacker is recalled.