Boss fight

I have a dragon boss that is made up of several entities. When the head entity (with tag snake.part.head) dies, I want to kill the rest of the dragon.
execute as @e[tag=snake.part.1,tag=!nocheck] unless entity @e[tag=snake.part.head,distance=..10,limit=1] run kill @s
execute as @e[tag=snake.part.2,tag=!nocheck] unless entity @e[tag=snake.part.1,distance=..10] run kill @s
execute as @e[tag=snake.part.3,tag=!nocheck] unless entity @e[tag=snake.part.2,distance=..10] run kill @s
execute as @e[tag=snake.part.4,tag=!nocheck] unless entity @e[tag=snake.part.3,distance=..10] run kill @s
execute as @e[tag=snake.part.5,tag=!nocheck] unless entity @e[tag=snake.part.4,distance=..10] run kill @s

This is my current function, but all the parts die when summoned