If you don't renew your Plan (fully pre-pay the cost of your Plan) then your account gets Suspended. No phone service. No Rewards. Add-ons (and unused funds, if any) remain on account but they cannot be used.
If your account is Suspended (remains unpaid) for 90 days then the account is Terminated. Closed. Permanently gone, poof, along with any unused Add-ons, unused funds, Rewards (Loyalty), SIM card (irrevocably deactivated), and phone number. At which point PM cannot reactivate or recover these things, it's built into the Telus billing system and beyond their control.
Public Mobile has no charges for account Suspension, Maintenance, or Reactivation. And does not charge you for a Plan (or issue Rewards) for the duration the account has been Suspended. If you deposit enough funds into your Self-Serve account to pay for your Plan before the account is Terminated then your Plan will be Reactivated (sometimes automatic, sometimes requires you click "Reactivate Plan") on day 1 of the billing cycle. Any remaining Add-ons will still be intact.