It depends on whether your GM considers a corpse to be a creature
There are already (at least) four other questions which delve into whether or not a corpse is considered a creature and/or an object:
Is there anything that is simultaneously a creature and an object?
What happens when I have a creature grappled and it dies?
What is the definition of "...
Since the spell states that the creature gains a movement speed, by them dying they are no longer to move using that flying speed, as a dead creature can't move of their own will. Since they would no longer be flying at that point, they would naturally begin to fall as they can do nothing to remain in the air.
Kelemvor would be very annoyed with that.
It is very likely that Doomguides: the powerful clerics, paladins and other followers would visit transgressor very soon.
If he transformed into undead to cheat death, you can bet Knights of the Eternal Order (or some adventures) would come knocking on his doors too.
Inevitables might have something to say too
Death Throes does not happen if you drop to 0 hit points
If you revert as a result of dropping to 0 hit points, any excess damage carries over to your normal form.
In other words, when you drop to 0 hit points you don't die, instead you directly revert into your normal form, so Death Throes does not take effect.
Death Throes might ...
You don't die so it doesn't trigger
In D&D, dropping to 0 hp doesn't necessarily mean that you die, especially if you are a PC. You can be unconscious (via non-lethal damage), you may have to roll death saving throws (via "lethal" damage), or, in your case, you may return to your original form.
And even if excess damage maked you drop to 0 hp, you are ...
No. The character reverts upon reaching 0 hp.
The most durable shape change, shapechange, states the target reverts upon getting to 0 hp.
If you revert as a result of dropping to 0 hit points, any excess damage carries over to your normal form. As long as the excess damage doesn't reduce your normal form to 0 hit points, you aren't knocked unconscious.