Is Zhonya's Hourglass effect mandatory when a unit dies, or can you choose when to activate it?

Ruling: Zhonya's Hourglass attempts to replace all deaths it sees. When a unit dies, you can choose to have Zhonya's replace that death (killing Zhonya's instead and following its instructions), but it is not mandatory if you have other replacement effects available.

Sequence:

• When one or more units would die while Zhonya's is up, its replacement effect triggers
• If multiple units die simultaneously, you can order the deaths to choose which unit Zhonya's saves
• If you have multiple "instead of dying" effects, you can order them to choose which replacement effect applies
• If another replacement effect prevents the death entirely, Zhonya's replacement effect won't execute and it won't kill itself

Nuances:

• Zhonya's only kills itself if its replacement effect is actually executed
• You have control over ordering simultaneous deaths and multiple replacement effects