In the fourth edition of the bat book I read:
Naturally, such a recovery should never be necessary if your machine is properly backed up, and if you keep your source files under some form of revision control, such as rcs(1).
Upon reading the passage, my memory triggered and brought to my attention again cvi, a handy little tool by Sotiris Tsimbonis just for this purpose.
Naturally.
Managing organized complexity 
Indeed, sendmail.mc was the reason I hacked cvi..
The passage that I copied was from a section about praliases and how it can be used to reconstruct /etc/mail/aliases from aliases.db when the text source is damaged or erased.