Comment by vault_

It's not "general purpose computing" maintenance, but the service you're talking about does exist, though AFAIK mostly at the very high-end. It's typically for things like home theaters, whole-home audio systems, or smart-home type setups (predating and now merging with current consumer IoT/home automation platforms). Not sure how much that's "maintenance" in the typical sense so much as support for their custom install work, but I bet if you had a Sonos or Lutron system where your installer went out of business you'd be able to find a different guy to deal with it.