“However, if the whole folder is deleted and the path is no longer accessible by Syncthing, the synchronisation will automatically stop. If only the contents are deleted, then the deletions will also be pushed to other devices.”
I’m not sure if there is any hierarcy with synced folders, but I tried this: deleted a folder and it disappeared also from another computer.
Specifically, deleting the folder marker, usually named .stfolder from folder A will stop the synchronization.
Operating systems / file managers usually start to delete a directory “depth-first”, which means the files may be gone and detected as deletions by Syncthing before the folder marker is even reached. If it’s a large dataset, recursive deletion may well take longer than the default watcher delay of 10 seconds.