You probably mean the case of doing so called "bomb-bestiary" -- Putting bombs at spawn places and just running around and refreshing the bombs (which is useful for 250 kill creatures, the easiest bestiary class). I want to add some screenshots:
2 months ago I did bomb bestiary on Laguna Islands and I unlocked almost all kind of frogs. Whenever you (or your party) does the most damage, you will always get loot messages, if the creature drops loot.
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If they don't drop anything, you will not get any loot, doesnt matter how you killed the creature, Some examples:
Here I killed black sheeps in Liberty Bay while putting bombs and standing afk on a safe spot:
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In the next screenshot I was close to the creature and did not get any loot.
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And as you can see in the following screenshot, I was far away from the ankrahmun tomb (and getting my level up because I made a special screenshot) but I definitely received loot messages, the loot window is blinking but the server messages channel is opened. Since the loot channel is blinking, you can see, I received loot. I deactivated loot messages for this moment in my game window so I cannot prove I received loot but the blinking should be a little proof
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All in all getting loot only depends on
- if the creature drops anything
- and if your damage or your party's damage was the highest
Consider, the last point must not be true for bosses, as far as I know.
It does not depend on how far away you are from the kills.
Another note: Field bombs do a constant amount of certain damage and frogs e.g. are killed in two stages: First they get deep red, then they die. And if they drop anything, you will get the loot message.
edit: the question was, if a creature drops loot if it instantly dies. On TibiaWiki:Fire we can see, that a damage of 20 hp is taken in one turn by a creature.
Regarding the creature list sorted by hitpoints:
we can see that there are indeed creatures being killed in only 1 turn but also dropping loot (such as spiders). Source: TibiWiki:ListOfCreatures
So my answer is: yes, creatures that die in one turn can indeed drop loot :)