Greetings, ["Kirsty McGurk"]!
Yes, you can deactivate bank accounts in QBO, and still be able to access other functionalities. The off-limits, when deactivating or disconnecting an account, are the following:
To learn more about the pros and cons and the steps on how, you can refer to this link: https://quickbooks.intuit.com/learn-support/en-us/banking/disconnect-or-delete-an-account-from-the-d...
I'm still here to help you more if you have follow-up questions. Just drop a comment or mention my name. Have a good one.