the idea of have two bios is that if the first one decides to do something weird and fail, the second one takes control while the first one restarts but the mainboard keeps running so you don't loose time or information in the process
afik, if the first one dies, the second one will not let the system boot, it is not a replacement for a dead bios, is just a backup for the moment of a possible error, which i must say is very uncommon, only for overclockers could be useful in reality