Yes, renaming a zone will impact all active sessions that reference it (in source and/or destination). When changing the name of a zone, the ID will change and all active sessions referencing the old zone name need to be cleared.
If change of zone name is needed, a maintenance window is recommended.
To clear all sessions on a firewall:
> clear session all
When renaming a zone, a new zone object (with a new name) is created in the background. A numeric ID is assigned to this new object created by the id-manager process. This ID will be used internally when referencing a specific zone, instead of the alphanumerical name.
To check the IDs assigned to zone names, run the following CLI command:
> debug device-server dump idmgr type zone all
Since id-manager objects are cumulative, all the zone objects created since the last reset will be shown.