Where router settings stored? What is EEPROM?

My question isn't related to OpenWrt directly. I just suspect folks there have enough experience to answer.
Recently I damaged Zyxel NBG6615 via telnet with command I don't remember. But now is fact, wi-fi disabled, it don't allow log into web-configureator with old pasword, and couldn't be reset to default password.
It based on Realtek controller "RTL8367RB -CG". I found in controller manual such words: "Supports 32K-byte EEPROM space for configuration".

I wonder is it enough to find same alive router model, get right SPI flash dump, and programm it.
Or my troubles situated only in EEPROM? (and have not related to SPI flash)

So, my questions is:
Is there the special EEPROM memory area inside controller, which didn't affected if 25xx SPI flash will be replaced with right firmware dump?
If it is, how usually it resets to default values? (when hardware reset button pushed)
Is that area affected when new manufacturer firmware being uppload?

Sorry if that stuff is offtopic. I'am newcomer here, appreciate to be guided right way, or may be other topic.