Somehow my K20samba4 was deleted.
How can I restore it (ie does anyone know where I can get the script)?
I don't think we ship a K20samba4 script anymore - samba 4 now uses upstart.
There is a /etc/rc4.d/S20samba4 file, which should be a symlink to ../init.d/samba4
update-rc.d should also be able to create it for you.