What happens when FortiGate is removed from FortiManager/FortiAnalyzer?

I am working a project which will see the customer inherit an existing FortiGate deployment. These firewalls reside in branch locations and are centrally managed using FortiManager in the data centres. They are also logging to FortiAnalyzer in the same location. 

My question is if the FortiGates are removed from FortiManager, will this impact the baseline configuration? My hope is that when removed from FortiManager, these devices can be locally managed with the configuration in tact.