Behaviour with 3 devices

I copied a part of all my mp3s from Dev1 (my main pc) to dev2 (my cloud server) (its not finished yet). when starting dev3 after a while offline what will happen… will the missing files (50) on dev2 be deleted?

Background story As I told here, there have been some files deleted in the following szenario: As described some time ago, I uploaded some of my files (eg 200) from dev1(master - 300 files) to dev2. after deactivating master on dev1 and syncing with dev2 (250 files) and dev3 thee have some files been deleted from dev1 (formerly master) and I do not know why. I didnt delete anything on the slaves… that’s why I’m trying to exactly understand how syncthing works and behaves in several situations…