First, I know nothing about VPN so keep that in mind when reading this.
My wife uses VPN when she works from home and as far as I can tell once the VPN connection is made it's as though she were connected directly to the work network. So in principle it should be the same as if you were trying to access a Windows share in a home network. Samba isn't configured to access remote shares, it's configured to offer shares on the linux box to others.
As for "mapping" you may have a problem there. The linux equivalent to windows' mapping a network drive is to create an entry in /etc/fstab for the remote share. It will mount the remote share automatically when your system boots and that's the problem. Even though the remote server may be up and operational your VPN connection hasn't been made yet so the mount will fail. There is a parameter you can add to the fstab entry - _netdev - that delays mounting the network share until after the boot process brings up the network, but the "network" is already up before you VPN. I need to think about this a little more. Hopefully there are others in this forum that have done this and can help you.
Let's start with basics first though, once you login to Mint and after you VPN can you see the Windows shares by going to Nautilus ( your Home folder on the desktop ) > Network ( under Places )?
EDIT: Alternate method - Bring up nautilus > File > Connect to Server > Service Type: Windows share
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