Aerial Assault — ruling 1

If the target creature is an illegal target by the time Aerial Assault tries to resolve, the spell doesn't resolve. You won't gain life. If the target is legal but is not destroyed (most likely because it has indestructible), you will gain life.

Aerial Assault — ruling 2

Any abilities that trigger as the target creature is destroyed won't resolve until after you've gained life.

Aerial Assault — ruling 3

If any creatures were exiled "until" the target creature left the battlefield, those creatures will return before you gain life.

Aerial Assault : règles, fonctionnement et interactions (MTG)

Aerial Assault is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Destroy target tapped creature. You gain 1 life for each creature you control with flying.

How it works : Aerial Assault

Original English text — Wizards of the Coast / Scryfall

#1July 12, 2019· Wizards of the Coast
If the target creature is an illegal target by the time Aerial Assault tries to resolve, the spell doesn't resolve. You won't gain life. If the target is legal but is not destroyed (most likely because it has indestructible), you will gain life.
No other card is named in this ruling.
#2July 12, 2019· Wizards of the Coast
Any abilities that trigger as the target creature is destroyed won't resolve until after you've gained life.
No other card is named in this ruling.
#3July 12, 2019· Wizards of the Coast
If any creatures were exiled "until" the target creature left the battlefield, those creatures will return before you gain life.
No other card is named in this ruling.