One option would be to export all your current macros, revert back to a point before you lost your missing macro and then import your newer macros.
FWIW, I use Library syncing and have the library file in my Dropbox so I have another option of rolling back my library.
However, I also use this amazing macro by @DanThomas to backup/restore individual macros and/or macro groups periodically. It has saved my bacon a few times.