Accidentally, by using a GUI as opposed to CLI, I removed every file in a Mercurial project.
I recovered with Revert ok and lost some work, which as I have time mach
For Mercurial 1.6 and above
If you know the name of the delete file you can find its revision easily with:
hg log -r "removes('NAME.c')"
This will give you the revision in witch a file called NAME.c (in the root) is deleted.
Then you can revert the file to the previous revision with (like other answers):
hg revert -r
You can use a file name pattern instead to adapt to what you know, for example you can use **/NAME.c
to search in all directories. You can read about it in File Name Patters. And use this link to know about the new revset specifications.