If you disconnect from QuickBooks Online you'll no longer be able to send your payroll data to your general ledger on QuickBooks Online.
If you want to reconnect, simply click the Reports menu from the top, then under Accounting Integration click Import Accounts or Export Files. This will restart the authorization process with QuickBooks Online.
If you've signed up for another accounting integration and you want to go back to QuickBooks Online, go to Reports > Accounting Integration and click Change Accounting Provider. You'll then need to go through the registration process for QuickBooks Online integration.