Back in PDP-11 days (Unix v.6) my boss managed to do a "rm -fr *" not in his personal bin (as he believed ATM) but in the system bin. Oooooops. (but Armando S was ready with functioning backups.)
I've been in a similar state - I had a shell running but lost /bin/ls among other things; but I could use "echo *" and redirection to recreate an /etc/mtab.