>So how do I get out of this with the things that are provided in
>/bin and /sbin?

/bin/rcp. If all else fails, rcp your gzipped tarfile somewhere you
can unpack it, then rcp the unpacked gunzip back to your /usr, then
untar the whole file using pax.

>If I can't, does it seem reasonable to add ftp and gzip to /bin so
>that it's easier to recover from such situations?

not for my taste.