well - if you don;t install any Spitfire apps, or Cubase, or Kontakt or (add in numerous everyday apps I use on my system), you can be internet-less but I use all these things and they check on startup, and some really need you to check in regularly to see what has been added, often free instruments and gizmos. It's just plain stupid to even attempt to run the more sophisticated stuff without an internet connection. Even more important when everything an application needs comes via the net, and for security, is checked each start up. Looking at the screen here now, Adobe have at least one update appeared today.
If you buy decent apps - they assume a permanent internet connection is available. If you don't have one, they don't work. I hear some people download on one computer, then transfer the files to another, then go back and get the next update and it works, but Cubase and Adobe - probably my most often used applications do not give you an internet free option. On top of this, there are more and more subscription services - like the excellent Roland historical synth one. However, the ones I would miss most would be Spitfire. Most weeks they give their customers new free stuff, new offer stuff and upgrades.
I see that some folks have their DAW's connected to the internet.
Some folk simply like to use software of their choice and have access to things they need. Being forced to only use certain applications and sounds is a real barrier to creativity. If you are paranoid about the dangerous internet wrecking your systems, then instigate security systems - off-site regular backups, and software to ensure they're done properly. Some restore software you trust for emergencies, and a virus protection service you can live with that isn't too draconian in saying compuyter says no.
What is the very worst that can happen? A user does a silly thing and doesn't pay enough attention and downloads that dodgy copy of the software from a site in Russia, and ecrypts their computer. Somebody else might have a single hard drive that fails spectacularly with the same result through no fault other than bad luck. You buy a new drive and start again, exactly the same as you could do if the worst internet virus had a go at you. Fix the PC, download your content and carry on.
The internet is part of life. Trying to avoid it puts you in a very small xenophobic club. Sure - there is a risk, but it's perfectly manageable.
I'm off overseas for ten weeks. My macbook holds really vital data for the job. This morning I've backed it up and put that back up on my older macbook. I have two identical machines. One will live in the office and the other in the place I'm staying. If something happens to macbook 1, I carry on using macbook 2 - and if the problem is terminal (as it was one year when one got smashed accidentally with a scenery truck) then I buy yet another, and put the backup on it.
If you are really worried about the internet - then really computers perhaps should not be what they are - just a tool. Would a carpenter not use his best chisel, on the chance he might uncover a nail? Just always use your second best one, just in case?