When we delete an account, its gone. There is no way to recreate or undelete it. So people which come back, need to make a new one.
And for sure, we cant tell people never to come back after they wanted a delete and i also dont want. I always hope these people come back, why not?
I also try to counter the new making of account with giving people 24h to think about a delete, before i delete an account. Mostly they stay then anyway. But sometimes, they delete and come back sooner or later.
About banned people... i always think people should get a second chance after an amount of time to overthink their behavior. For sure, the duration of acceptance is then way shorter and if they fall back in the old behavior, its done pretty quickly. But i like people to grow from their mistakes. Maybe i am to optimistic here, but yeah.