If the spell that triggered
Hive Mind or
Zada, Hedron Grinder's abilities has left the stack before the trigger resolves, the copy the trigger creates will be based on the last-known information of that spell as it was on the stack. The same holds true for similar effects that copy spells without targeting them, such as (famously) the Storm ability, and most recently
Doublecast.
This happens because when the ability resolves, it checks the game for information about the spell it wants to copy. Normally, the spell's current information would be used for this, but since the spell is no longer in the zone it's expected to be in (the stack), it doesn't have any current information to be referenced and its last-known information is used instead–its information at the last time it was in the expected zone.
The relevant rule here is from the section on Resolving Spells and Abilities (CR 608), specifically 608.2g:
608.2g If an effect requires information from the game (such as the number of creatures on the battlefield), the answer is determined only once, when the effect is applied. If the effect requires information from a specific object, including the source of the ability itself, the effect uses the current information of that object if it’s in the public zone it was expected to be in; if it’s no longer in that zone, or if the effect has moved it from a public zone to a hidden zone, the effect uses the object’s last known information. See rule 112.7a. If an ability states that an object does something, it’s the object as it exists—or as it most recently existed—that does it, not the ability.