This is more of an IT/Networking question, since neither using Perspective or the WebDev module will make the screens publicly accessible. Even if you converted to Perspective or the WebDev module your clients would still not be able to use the screens without a VPN since the organization’s network is isolated from the public.
The (kind of) good news is you can solve this issue without moving away from Vision, by placing the Ignition Gateway in the Cloud or in a DMZ. This would allow your clients to install and use the Vision screens from anywhere in the world. It’s important to note that this is inherently insecure and definitely not recommended because anyone can now attempt to hack into the SCADA system from anywhere in the world without needing VPN credentials. This is what a VPN was invented for and it’s recommended to use it as is.
I would recommend talking to the IT department about this. They will most likely not feel comfortable exposing the SCADA gateway, but may have other options, such as temporary logins, to make it easier for outside users to see the screens.