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.
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:
In the next screenshot I was close to the creature and did not get any loot.
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
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 :)