Comment 10 for bug 1508697

That situation should never arise, because if the symlink exists, then it was created by a successful boot with systemd sometime in the past; systemd's API is that it guarantees to create /etc/machine-id before running third-party code; and systemd never deletes the machine ID after it has created one.

The ideal behaviour would be for dbus-uuidgen to replace the symlink with a newly generated plain file, I think. I'd be happy to review a patch (on freedesktop.org Bugzilla please) if that isn't already what it does.