[bremac]

The internet is the least of your problems. The key industrial automation equipment (PLCs and IPCs) is connected directly to your machines. Higher-level control and planning functions like MES and SCADA are usually running from your server closet. You might not have access to your ERP or cloud MES system, but you can keep the lines running without them for a while. Plenty of factories have weak or flaky internet, so operating during an internet outage is hardly a novel situation.

Your bigger problem is the supply chain. After the apocalypse, I doubt you'll have an easy time sourcing cans, bulk product, spare parts, and sanitizer to run your factory. After all, each of those inputs to your process have their own complex supply chain too. And no, you're not really going to be able to scavenge these parts of manufacture them yourself, since they all have fairly fine tolerances.

In reality, I'd expect that an apocalypse will cause a reversion to a more subsistence-style lifestyle, where production and consumption are largely local and supply chains are very simple, if present at all. Computers will not help with this. I can't imagine keeping our current production processes running without all of the things required to support them.