If an attacking unit with Assault moves into a battlefield and the defending unit is moved out before combat resolves, does the attacking unit still get the Assault buff and survive damage marked on it?

Ruling: Yes, combat resolves regardless of the defender leaving the battlefield. The attacking unit retains its Assault buff and will survive any damage marked on it during combat.

Sequence:

• Attacker moves into battlefield and attackers/defenders are declared
• Assault buff is applied to the attacker
• If defender leaves the battlefield during combat, the attacker keeps its Assault buff
• Combat resolves with the attacker surviving

Nuances:

• The Assault might increase is only removed at the battlefield of combat during a specific cleanup step
• Attacker/defender designations are removed during Cleanup if units leave the battlefield of combat, but this doesn't affect buffs already applied