Dns Vpn Ipsec Dial up

Hello I would like your help regarding a doubt I have about the operation of the dns on a windows machine when a vpn connection is made through the forticlient. There is a vpn client to site and when the connection is made, routes are received to a server and to a computer with the dns service (the split tunnel is enabled), so when a query is made an nslookup to the dns registers me the dns configured in the vpn this because the interface has a higher priority, however it happens with the other dns queries made to the other destinations, they have to be sent to this server to the vpn and when a response is obtained they will go out its connection to the isp of the network card. In case all the queries to the Dns travel by the vpn BUT the configured dns had faults I would not have way to solve with the dns of my isp and I would be without internal until it makes the disconnection of the vpn.

Thank you

note :In the images the explanation