Will existing permissions and ownership be restored after the device is replaced?
Yes, only in the case of AD users permissions and ownership will be restored as they were on the source device on both Windows and Mac.
What happens if the Druva inSync Server is restarted while the device replace is in progress?
If device replace process coincides with Druva inSync Server restart, the process needs to be reinitiated.
What will happen to the old device when the device replace process is triggered.
The old device will be deactivated and inSync Client will stop working on it.