How to delete Windows NTFS hard link (mklink /h) while original is in use?

This is quite expected behavior, the hard link is just another name for the same file. E.g., if you have file A.PDF, create hard link B.PDF to the same file, it doesn't matter whether the file is opened under the name A.PDF or B.PDF - it's still the same file, so if this file is simply opened, you can't delete either link.

The actual reason is that the name is stored as an attribute in the file record of master file table (in case of NTFS) and since the file is opened, you can't delete either link (you can't modify opened file).

In this case there's nothing like original file, since both names belong to the same (and the only one) file and both names are equal. The file is actually deleted when link count reaches zero.

Use the FSUTIL tool to maintain the symlinks safely.

http://technet.microsoft.com/en-ca/library/cc753059.aspx

fsutil reparsepoint delete link.mp3

would remove the hardlink while preserving orig.mp3