Accidentally unloaded all launchctl daemons and now can't boot
for a persistent fix you can login to single user mode, then mount -uw /,
and then delete the launchctl override database.
I'm not sure for Yosemite, but on Sierra that would be rm /var/db/com.apple.xpc.launchd/*.plist.
after that you can just exit or reboot.
this is not as a sledgehammer as it seems. the system re-enableds some of its overrides (from various other configuration files i guess) and so you actually get a nice and fresh override db without masses of "disabled: false".