The pool is and was in no way connected to the home. The entire premise and ordinance city is referring to states, an accessory use building (which the pool falls under) can not exist without the main use building (home). Although the actual ordinance states the accessory use building can not be "built" without the main. It says nothing about having to destroy a perfectly good accessory building. Essentially, even if it were a $100k pole barn, they would force us to destroy it.The OP says "the pool meets all safety requirements". We are taking that at face value, but I'd like to find out more.
Years ago I saw where a house burned down but the pool remained. The former wall of the house had formed part of the pool's perimeter safety fence. The owner fenced off the perimeter of the site, but not with the kind of fences that met pool code.
Also, without power (the house panel burned up) the water circulation stopped, the owner stopped maintaining the pool, it got algae, then they eventually had mosquito vector control issues.