How are further structural failures prevented if an aft pressure bulkhead fails?
If what's escaping a compromised bulkhead is cabin pressure, not an explosion; the airframe structure aft of the pressure vessel is wide open for air to escape.  The structure is hollow from one component to the next with "lightening holes" wherever possible designed to minimize weight (nothing to do with thunderstorm lightning).  Additionally, the lightening holes provide for plumbing, wiring, maintenance, inspection access, and ventilation.

Unless there's an explosion or some catastrophic failure of the pressure vessel, escaping cabin pressure by itself cannot pressurize the open empennage.  Pressurized aircraft also have a safety valve to protect the pressure vessel from structural damage in the event of outflow valve failure.  The prospect of aft pressure bulkhead failure before other skin fracture is unlikely.

If you are able to peer in between the rudder and vertical stabilizer of an aircraft, you will likely see the openings.