I think that this is exactly what NAT does. The host just acts as a router with Network Address Translation from the guest onwards out to the network the host is connected to.
If you want a network connection to the guest that will not do this and will not be lost if the host cannot get a network connection (i.e. to a WiFi router) then I think your only option is host only networking.
This isolates the connection between host and guest from all other connections but it stays put no matter what.
On the downside: The guest will not have Internet access.
I have used this a lot when I did not want to use bridged networking since it would clutter up the router (especially at customers) and my only need was to be able to communicate host-guest.