If you forget a network does the address and password get erased?

This is absolutely correct in 99% of the cases, when the Wi-Fi router broadcasts its SSID. For privacy reasons, some people set their router not to broadcast it, in which case a forgotten network will not reappear in the list of available networks: one would have to enter the exact name of the network in order to reconnect to it.

The Wi-Fi network is dropped. It can be found again.