UNIX for Advanced & Expert Users

Provided he has a backup of the file

It is after the fact, but in the future you can attempt a recover by forcing the editor to preserve your buffer. You will find this useful if you have made edits, then discover that you can't save your edits. You can then use the vi -r <file> to recover the buffer after you close.

If the file system is full you can also delete something with :! rm <junkfile> the !(bang) allows you to issue unix commands within the editor, like : !df to see the space.

Best case, write the file to a directory in another filesystem that has space available with :w /usr/local/../.../file

Daivd