Here is a Spell I created, I noticed that it works as intended WHILE the caster is alive. However, if the caster dies, the duration on the Flight disappears and players are left floating in place until killed.

AoEImmobilize:
actions:
cast:
- class: AreaOfEffect
actions:
- class: Velocity
direction: 0,0.2,0
- class: Delay
delay: 100
- class: PotionEffect
duration: 3000
add_effects:
SLOW: 7
- class: Fly
duration: 3000
speed: 0.001
effects:
cast:
- class: EffectSingle
sound: kitpvp.freeze
location: origin
color_override: color
source_location: body
effectlib:
class: Sphere
particle: smoke_normal
radius: $radius
height: 3
enable_rotation: true
particles: 60
speed: .1
duration: 500
disappear_with_origin_entity: true
parameters:
cooldown: 12000
target: self
radius: 7

Hopefully, there is something that can be done about this :)

cancel_on_death: true
or add an undo parameter

Thank you @PhvntxmX - @GrantisMantis did that work for you? I think cancel on death is what you want.