When a unit is stunned attacking a battlefield but isn't killed, what happens?

When an attacking unit is stunned during combat but is not killed, the outcome depends on whether any defending units remain at the battlefield after combat concludes.

According to Rule 461.1.a.2 and FAQ 7302, if defending units are still present at the battlefield after combat, the attacking units are recalled to their base.

In summary:

• If defending units remain: The attacking units are recalled to base (Rule 461.1.a.2).
• If no defending units remain: The stunned attacking unit remains on the battlefield and successfully conquers it, as stun only prevents dealing combat damage and does not prevent conquest (FAQ 3409).

Note that being recalled in this manner does not count as a move (FAQ 6909).