What will happen in this scenario?
It will delete the subnet and make the EC2 instance as a part of the default subnet
It will not allow the user to delete the subnet until the instances are terminated
It will delete the subnet as well as terminate the instances
The subnet can never be deleted independently, but the user has to delete the VPC first
Explanations:
Deleting a subnet does not automatically move the EC2 instance to the default subnet; instances must be manually moved or terminated.
AWS does not allow the deletion of a subnet that contains active resources, such as EC2 instances, until those instances are terminated or moved.
The deletion of a subnet does not automatically terminate instances within it; instances must be terminated manually or moved to another subnet before deletion.
A subnet can be deleted independently of the VPC, provided it does not contain any resources. The VPC itself does not need to be deleted first.
I rate that the answer is:
It will not allow the user to delete the subnet until the instances are terminated