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Let me share some information on how deleting your sub-customer or customer affects your QuickBooks account.
When a customer or sub customer is deleted, you'd see a Deleted tagged beside the name of the customer or sub-customer. 
Just a heads-up though, when a non-zero balance sub-customer is deleted, the system will automatically create an adjustment transaction. This will zero-out or offset the sub-customer or customer's balance.

You can view the report so you'd see the details of the adjustment transaction.
Once you reactivate the sub-customer, you'll still see the same list of transactions associated with it. However, its balance will become $0.00. 
You can refer to this article to learn more about managing your customers and sub-customers: Sales and customers.
Also, you can visit our blog for the hottest features and helpful tips on how to boost sales during slow season: The QuickBooks Blog.
Feel free to visit us here if you have other questions or concerns. I'm always here to help.