File sync after backup recovery

just a little question regarding my desaster backup recovery.

I am using ncp on an ODroid HC2 with an SD-card to boot and everything else on the attached HDD. As a last resort backup I am cloning the SD-card and the hard drive monthly at the same time. In case I revert my broken server to the backup media and there are newer files on the clients which have been synced to nextcloud after creating the backup images how will the server respond?
Will it delete the newer files on the client because the server dont knows them or will it sync them a second time to the recovered server?

For better understanding a little example:

Step 1: Files 1 and 2 on client, synced to server
Step 2: Creation of server backup
Step 3: Files 3 and 4 created on client and synced to server
Step 4: broken server -> backup recovery (server now only knows files as in step 2)
Step 5: Client sync -> What happens to Files 3 and 4?

Thanx for any hints.
Kind regards, gst