In a multiplayer game, if you attack a player who then concedes, do your attacking creatures go back to untapped or stay in combat?

When a player concedes during a multiplayer game, they immediately leave the game. All permanents they controlled are removed from the game, and all spells and abilities they controlled cease to exist (CR 800.4a). However, the attacking creatures themselves are not removed — they remain in the combat zone, still attacking.

Critically, CR 506.4 states that when the defending player leaves the game during combat, any creatures attacking that player are removed from combat. They do not return to an untapped state — CR 506.4 specifies that attacking creatures that are removed from combat in this way stay tapped. They simply are no longer considered attacking anything.

This is different from simply losing the combat target. The creatures do not untap, do not deal combat damage, and do not trigger any 'whenever this creature deals combat damage' effects. They just sit tapped on the battlefield until your next untap step (barring other effects).

Concrete example: You attack Player B with a 3/3 and a 2/2. Before blockers are declared, Player B concedes. Both creatures are removed from combat, remain tapped, and deal no combat damage. On your next turn, they untap as normal.

Note: If you had attacked multiple players (allowed in some multiplayer formats), only the creatures attacking the departing player are affected. Creatures attacking other players continue in combat normally (CR 800.4a, 506.4).