The VPN Killswitch is built in to the connection state. If you have the VPN enabled and the tunnel goes down (connection) then it will be killed.
If you disable the VPN client then the client will be able to talk over the clearnet (WAN) as the VPN rule will no longer be enforced.
I personally made a rule whereby a client that I have policy based routed should always be disconnected even if the VPN option has been disabled, you can visit my post here