{Celestial flare}
Opponent declares attackers, I cast this, does damage resolve?
The damage from the sacrificed creature won't be dealt to you.
Also, (I'm just saying this because of the way you worded your question), damage doesn't use the stack anymore. It's now dealt in the combat damage step.
Celestial flair doesn't cause damage. From the phrasing of your question I wasn't sure if this was part of your question or not.
To answer you question, yes, damage still resolves. The sacrificed attacking creature, however, won't be around to contribute to the damage.
Quote from: E.kann1 on March 01, 2014, 08:20:00 AM
The damage from the sacrificed creature won't be dealt to you.
Also, (I'm just saying this because of the way you worded your question), damage doesn't use the stack anymore. It's now dealt in the combat damage step.
Listen to this one
506.1. (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=506.1.): The combat phase has five steps, which proceed in order: beginning of combat, declare attackers, declare blockers, combat damage, and end of combat. The declare blockers and combat damage steps are skipped if no creatures are declared as attackers or put onto the battlefield attacking (see rule 508.4). There are two combat damage steps if any attacking or blocking creature has first strike (see rule 702.7) or double strike (see rule 702.4).
So, he declares attackers and passes priority. You cast celestial flare, he sacs a creature. It then moves to declare blockers, and that creature is no longer around. In short, the creature would not be around for the combat damage step.