If a single card effect kills both an enemy unit and Zhonya's Hourglass simultaneously, can Zhonya's Hourglass save the unit?

Ruling: If a spell or ability kills a unit and gear simultaneously with a single effect, the order matters. If the effect is templated as "kill an enemy unit and an enemy gear," Zhonya's replacement effect can replace the unit dying. If it's "kill an enemy gear and an enemy unit," Zhonya's cannot save the unit because it's destroyed first.

Nuances:

• Replacement effects can "see" through the steps and events of a spell or ability resolving, so the order of game actions within a single effect matters
• This only applies to spells/abilities; if both were leaving simultaneously due to a trigger, Zhonya's could not intercede in either case
• There is uncertainty about whether replacement effects can apply when events happen truly simultaneously (as opposed to sequentially within a single effect)