Sack Tor Aendris ( Quest. Any unit questing here may attack as though it were in your battlefield. Quest. You may spend resources on this quest to pay for cards and effects. Quest. Forced: At the end of any turn in which the questing unit participated in an attack, place a resource token on this card. )

Altar of Khaine ( Kingdom. Action: If one of your units would be destroyed, you may pay 1 resource to instead return it to your hand. )

I have both of these in play, with a unit currently questing on Sack Tor Aendris and 2 resources on the quest. That unit is assigned fatal combat damage. Can I use the resources on the quest to pay for STAs ability? Or do the resources clear because a unit is no longer on the quest.

I assume that you can use the resources, because Altar says "would be destroyed" so the unit is not yet destroyed, and so is still on the quest. I'm really unclear, however, on when Altar actually triggers. In the rules, it says actions " can be triggered by either player during any action window in the game sequence " The only action windows that could be relevant are right before and right after damage is assigned and characters leave play . In the first window, the unit is not assured of being destroyed (though it may have fatal damage assigned) and in the second window it has already left play.

The FAQ offers some more information about "response actions" but still only gives an example of a unit whose Action triggers during a normal action window.

If the Altar triggers during something that is not a "normal action window" can you still play actions in response to it triggering? The basic rulebook seems to indicate you can " actions can also be played or triggered in response to other actions ".

You can use the resources that are already on Sack Tor Aendris, because the Altar kicks in before the unit it destroyed so the resources are still there. One the unit has been returned to your hand, any other resources remaining on the quest will be lost as there is no longer a unit questing there.

Thanks. Can you elaborate on the timing of using "would be destroyed" triggers? Where is the unit when this occurs? Still in play or in a "between in play and discard pile" state?

Technically still in play. The trigger is the point at which your unit would be removed from play and sent to the discard pile, most likely due to applied damage or a "destroy a unit" card effect, and the unit goes to your hand instead so although it's in play when the action is played it's not once it's resolved. It's worth noting that this is an action that you play as a reaction, so it's outside the usual action windows.