tdtracer - is there any level of engine protection on the engine itself? That is, at a level below the FADEC controller(s)?
It depends on the engine. It's required by the regulations that the engine be protected against an uncontrolled overspeed condition. As I noted, some FADEC engines have a hydro-mechanical fly-ball governor that will hold the N2/N3 rotor just above redline (it's assumed if the high rotor goes over redline and stays there, something pretty serious has gone wrong with the FADEC's ability to control the engine) - if somehow the FADEC regains control the engine will subsequently react normally below redline. The CF6-80C2 FADEC, GE90, and RB211-524G/H fall into this category. The PW2000 has an interesting variation - it's has a fly-ball governor, if N2 goes over redline it trips a mechanical circuit and the governor will hold N2 at 85% N2.
The PW4000, Trent (at least on Boeing installations), and the GEnx use an electronic overspeed protection - details vary but there is an independent circuit in the FADEC that if N2/N3 exceeds a set value it'll close the fuel metering valve (completely in the case of GE and Rolls, min flow stop for the PW4000). Once activated the electronic overspeed is latched, the FADEC must be reset to unlatch it.
Rolls has an additional electronic system on the Trent - the Rolls three spool design makes bearing design particularly tricky, and there have been cases where a bearing failure has sheared the shaft between fan (or compressor) and the turbine, allowing the turbine to accelerate uncontrolled and burst. So the Trent has a specific "Turbine OverSpeed" protection" (TOS) that monitors the rotor speeds at both ends - if they differ it'll shutdown the engine.