How do "fundamentally unstable" aircraft deal with the risk of computer failure?
"fundamentally unstable" but über-responsive aircraft have multiple computers that take a vote on everything the pilot wants to do. If one computer fails the others will take over. There is often no direct connection between the control column and the flight surfaces so the "no computer aid" situation would be the same as #2.

If everything fails, the checklist is rather short: eject immediately.