What happens when I delete a non-posting pending invoice

Yes, when you delete a non-posting pending invoice in QuickBooks Desktop, all linked time and costs will automatically become billable again. 
 

Since pending invoices are non-posting, they do not affect your financial ledgers. Deleting one disconnects the link, instantly returning your time entries, items, and expenses to your pool of unbilled records so you can apply them to future invoices.
 

Let us know if you have further questions or concerns.