You could add an extra condition to the overlaps event thats triggered to destroy the rocket:
condition : object thruster, pick nearest rocket.X rocket.Y
action: destroy thruster
The container should work best though, it should destroy the thruster created with the rocket.
Building the container is easy.
Select the rocket, in the propperties bar click edit container, and add the thruster.
Next when you create a rocket, the thruster is created too.
I always use an objects layout, and place my thruster already on the position it should be. when the new rocket gets created, the thruster is already in place as I did on the objects layout. Only requiring me to pin it after creating the rocket....
Hmm, wasnt the container a paid feature ? I forgot -,-