the story is as follows:
There is something more than just a second bios chip. There is a copy of bios contents stored in the HDD connected to the MB, this function is called Express BIOS Rescue or just Virtual Dual BIOS.
On every boot up of the MB, it checks the hard disk if there is any bios image inside it.
If there is no bios image into the hard disk, the current main bios version will be saved into hard disk (inside the special hidden area, not available to standard OS).
That means the hard disk has the same bios version like the main bios.
If the main bios is damaged, the bios contents will auto rescue from hard disk.
If there is no hard disk, then it will recover from backup bios.
If you upgrade the hardware main bios chip, then at next boot the copy of bios in HDD is also updated automatically.
In the situation you describe nothing wrong will happen, just bios will be recovered from HDD and system will work.
Hope this is clear explanation
To have a copy of BIOS on your HDD you need to enable the following option in the BIOS:
"Backup BIOS Image to HDD", which can be found under Advanced BIOS Features