Chain Assassination
Instant
Freerunning 
(You may cast this spell for its freerunning cost if you dealt combat damage to a player this turn with an Assassin or commander.)
Destroy target creature. If another creature died this turn, draw a card.
"Who needs stealth when there's no one left to raise the alarm?" —Jacob Frye
Filipe Pagliuso
Assassin's Creed (ACR)
• #23Rulings
Once an Assassin creature or commander you control deals combat damage to a player in a turn, you can cast spells for their freerunning costs for the rest of that turn. It doesn’t matter what happens to that Assassin or commander after that.
(wotc • 2024-07-05)
If the target creature is a legal target but isn’t destroyed, most likely because it has indestructible, you’ll still draw a card if another creature died this turn.
(wotc • 2024-07-05)
If the target creature is an illegal target by the time Chain Assassination tries to resolve, it won’t resolve and none of its effects will happen. You won’t draw a card even if another creature has died this turn.
(wotc • 2024-07-05)
Rulings
Once an Assassin creature or commander you control deals combat damage to a player in a turn, you can cast spells for their freerunning costs for the rest of that turn. It doesn’t matter what happens to that Assassin or commander after that.
(wotc • 2024-07-05)
If the target creature is a legal target but isn’t destroyed, most likely because it has indestructible, you’ll still draw a card if another creature died this turn.
(wotc • 2024-07-05)
If the target creature is an illegal target by the time Chain Assassination tries to resolve, it won’t resolve and none of its effects will happen. You won’t draw a card even if another creature has died this turn.
(wotc • 2024-07-05)