No, copying the files is not a good idea, ever. The system accounts (uid/gid less than 500) should not be altered. User accounts can be manually edited in, if you are careful to keep the files consistent, and manually created the home directories.
You will need to restore the files that were overwritten. I assume, since you have a sysadmin, that backups were taken before any manual modifications to system files. If not, it's time to get a new sysadmin.