I dont think VPNs are the correct solution. They are one solution, sure, but if it is the correct solution depends on many things.

For example, where does the VPN connect to? The vendor? Do you trust the vendor more than the internet. Sure. Do you trust the vendor, that does not manage the firmware of their devices and uses inbound connections in the first place, enough to put them on a VPN?

How many devices and vendors do you have? How many VPNs can you establish with the existing networking hardware, and how many can you manage without IP clashes etc. IP clashes work both ways, btw. The vendor has to manage this themselves also if all their clients want VPNs.

Retailers are enterprises with 100s of vendors that run on a shoestring. On top, they use a lot of legacy architecture and hardware. They have teams that have a hard time making an architectural decision in the best of times, but even less so under stress. It is probably the same on the vendors side.

In my mind, the correct solution is indeed to deny any inbound connection to the network, now, to prevent further damage.

Incident response is, in order:

    1. preparation (failed)
    2. identification (done)
    3. containment <--- we are here (take offline, put manual rota in place to manage fridge defrost cycles) 
    4. eradication (VPN, etc)
    5. recovery (take it back online, relieve manual rota)
    6. postmortem etc