If a creature is flickered during the declare attackers step, do its attack triggers still resolve?

When a creature is declared as an attacker, it becomes an attacking creature and any 'whenever this creature attacks' triggered abilities trigger at that moment (CR 508.1). Those triggers are placed on the stack and wait to resolve, but the creature remains an attacking creature in the meantime.

If the creature is then flickered — exiled and returned to the battlefield — it becomes a new object with no memory of its previous existence (CR 400.7). A new permanent on the battlefield is not an attacking creature unless something specifically puts it into an attacking state, so it is removed from combat (CR 506.4).

Because 'whenever this creature attacks' triggers only trigger when a creature is declared as an attacker (or is put into the attacking zone by a spell or ability that says it's attacking), the creature's re-entry does NOT cause those triggers to fire again. However, any triggers that already went on the stack BEFORE the flicker still resolve normally, since they were already captured.

Concrete example: You attack with Hero of Bladehold. Before its 'when ~ attacks' trigger resolves, your opponent flickers it with Otherworldly Journey. The creature returns as a new object, is no longer attacking, and the trigger that was already on the stack still resolves — but the returned creature does not generate a new trigger because it was never declared as an attacker this combat.

Key rules: CR 400.7 (objects changing zones lose history), CR 508.1 (attack triggers happen at declaration), CR 506.4 (creature removed from combat when it leaves the battlefield).