Peltier high limit temperature
Would a temporary failure happen, if so what temperature and 


From the FAQ at the TE Technology website:

The maximum ambient temperature will depend on the desired reliability, the heat sink, how much heat is being dissipated, and the temperature rating for the module or other system components (such as fans and insulating materials). Typically the maximum ambient temperature is limited to approximately 50 °C for standard coolers that use fan-cooled heat sinks. Coolers that use high-temperature modules are able to operate at higher ambient temperatures though. However, most commercially available fans have a maximum operating temperature of -10 °C to +70 °C. Be sure to consult with us to verify whether operating in higher ambient temperatures is possible.


  is there a permanent failure temperature, whereas the device is permanently destroyed.


Typically if you heat it up too much, the solder joining the p- and n-type semiconductor elements together will fail. Often the solder used has a relatively low melting point, so the limit temperature is lower than the 188 C you would expect if ordinary tin-lead solder were used.