We no longer work with a vendor but still showing invoice due this month shoud I delete their invoice?

Thanks for reaching out to the Community, @brianansari. 

Before going into detail, I want to ask if you mean how to delete a bill?

In QuickBooks Online, invoices are generally used for customers and bills are what you pay to vendors. I recommend paying the bill that's owed before deleting it. 

For now, below are instructions with how to delete a bill:

1. In the left menu, select the Expenses tab. 
2. Locate the bill from the Expense Transactions list. 
3. In the Bill page, click More at the bottom. 
4. Pick Delete from the pop-up menu. 
5. When you're ready, choose Yes to confirm that you want to delete the bill. 

For detailed info with deleting a bill, refer back to this article: How to delete a bill.

I look forward to chatting with you soon. Have a safe and productive rest of your day!