Impact in Collections changing Customer account to Inactive

Business wants to turn off the customer accounts to inactive to prevent further the billing. We already have implemented advance collection and strategies are determined at the Account level.

what will be the impact on the collections if the customer still has the past due invoices needs to be collected.

how can we send the dunning letters to the inactive accounts.

Is the customer information can be updated from the collector workbench on the inactive account.

Thanks in advance