Not sure how late this is, but there are a few ways you can disconnect [hard] from the net without actually touching the box; in order of increasing desperation (for next time).

1. /etc/rc.d/init.d/network stop (unless hacked, should stop all network resources).
2. use ifconfig to take the ethernet (?) interface down
3. If using lkms (assumed since you're using RH), you may be able to unload the ethernet module using rmmod.

About the x-sessions to administer a system -- forgive my ignorance here, but I was under the impression that if you opened X over a properly encrypted ssh session, X was encrypted too... If not, I guess it's good I only do this over a private subnet!