Reinstall bash on MacOS 10.7
If this someone did everything which is documented in the referenced article, you should be able to get your old bash back by 


Opening Terminal.app (which will give you an error because it can't start bash)
Running another shell directly via "Shell -- New Command" (Shift-Cmd-N) (e.g. /bin/ksh)
Executing sudo mv /bin/bash-old /bin/bash