Imagine that the conjure animals spell has been used which includes the following text:
[...] Each beast is also considered fey, and it disappears when it drops to 0 hit points or when the spell ends [...]
In the comments to this question about homebrew spells the following was stated:
Looking at all summoning spells: They have the line "Each beast is also considered fey, and it disappears when it drops to 0 hit points or when the spell ends." This means they do not die [...]
I'm wondering if this is actually the case, when a summoned creature is reduced to 0 hit points has it actually died?
I would like answers to assume that summoned creatures do not make death saving throws (otherwise they wouldn't be dead and would disappear to go make their saving throws and it gets somewhat messy).
Also note that this is specifically about summoned creatures as they have the rather unusual behavior of disappearing when dropping to 0 hit points instead of the usual thing that monsters do (staying put). I'm unsure if there is something in the books about whether they count as having died when doing this.
An example of where this matters is the Hexblade Warlock's Hexblade's Curse feature:
[...] If the cursed target dies, you regain hit points equal to your warlock level + your Charisma modifier (minimum of 1 hit point) [...]
Would they gain this benefit when a summoned creature is reduced to 0 hit points?