If you use a reaction heartbeat on an attacking unit's ability, does the ability still resolve if the unit dies? Specifically for Yellow Rek'Sai Swarm Queen.

Ruling: When a trigger is put on the stack, it will resolve even if the unit dies, unless the ability requires the unit to be "here" (on the board). For Yellow Rek'Sai Swarm Queen, the ability would resolve, but you cannot play the unit at Rek'Sai's location because "here" returns null when Rek'Sai is moved to a non-board zone (like the trash).

Nuances:

• "Here" can only refer to locations on the board, not zones like trash
• Abilities that require the unit to be "here" (like Lucian's damage) will not resolve if the unit is killed
• "May play it here" means it is another valid location to play the unit (in addition to normal play locations like base), but the choice is optional