A number cannot be ported out without the Public Mobile account getting closed. This is an automatic process. It will happen. The rules of number porting state that Public Mobile most close out your phone line/service/account when you port out. They are mandated to do that.
Saying that, the closed account doesn't have to necessarily be a permanently closed account. Technically, a new phone number could be assigned to the account and the account reactivated, but that would have to be done after the other number has first been transfered out.
Public could always create a new account for you and assign your old plan to you (if CS has access to the old plan).
Realize that the company is under no obligation to do any of that. While making some type of accomodation for you could likely be arranged, the answer could still be "no". There could be technical limations that get in the way, and even if there isn't, there are sometimes business rules and decisions that customers service needs to abide by.
