To lock bootloader you have flash your stock firmware, which in a way would be a complete reset, so no root left. Also, whatever you do after with the phone, once you request the unlock code from the moto website, they will consider your phone unlocked, hence no warranty. You can relock to try your luck and they just might not care if you are lucky.
Be very careful with locking bootloader though, locking your bootloader in a wrong way (wrong firmware, not flashing all files, downgrading) will create a big mess. In my opinion, stay away from locking bootloader!