For those off times when you delete the whole city (and not just the plots) during the self destruct sequence (IE when conqueror pre-builds a city you don't want it to but for some reason it decides to anyway) it still leaves all the (non-unique) settlers and/or civilians running around in a now empty city. While I can see the reason for this (for if you want to reassign them to a different city or keep them around to get a headstart on your new settlement build) I think it should give you the option to boot all the settlers/civilians as well if you select "Destroy it all!" once it's done. Like, again, if it built up Red Rocket Truck Stop when it really should not have and you're not ready to start sim settlements just yet. That way, should you want to boot all the settlers permanently, you won't have to hunt them all down.