Now that the synchronization has stopped, here's what's going to happen:
Your contacts from CentrixOne will not be sent to QuickBooks Online anymore. Alternatively, your customers from QuickBooks Online won't be sent to CentrixOne anymore either.
Your invoices from QuickBooks Online will not be added to CentrixOne as Sales (opportunities at 100%) anymore.
Your product types from QuickBooks Online will not be added to CentrixOne as "Revenue categories" anymore.
The information that you now have in CentrixOne that came from QuickBooks Online, meaning your clients, invoices and product types will remain in CentrixOne in the list called “Quickbooks.” If you wish to delete them, you'll have to do so manually.
The information that you now have in QuickBooks Online that came from CentrixOne, meaning your contacts, will remain in QuickBooks Online unless you delete them manually.
If one day you wish to reconnect the two apps together and you haven't deleted any information, the synchronization will pick up where you left off, meaning that what hasn't been synchronized will now be and what was already synchronized will not create duplicates.
If you do wish to reactivate the QuickBooks Online - CentrixOne synchronization, you can always do so by going to Settings→QuickBooks Integration →Synch Now.