Hi there, landscapingservi.
Thank you for reaching out to the Community.
Yes you can still keep the QuickBooks Desktop. However, when you run an invoice or any transactions from QuickBooks Online it wouldn't sync in QuickBooks Desktop.
You can check out this article on how to use the features and functions in QuickBooks Online: Getting started with QuickBooks Online.
Just in case, I've attach this article for comparison between QuickBooks Online and QuickBooks Desktop: Compare to see how QuickBooks Online delivers.
Let me know if you need more assistance with this. I'll be around to further help you. Have a great day!