The machines from decades past had a manual cleaning cycle that included draining the system, partial disassembly and disinfection of parts. Most assistant store managers (and some shift managers) are/were trained for this job. Of course most other restaurants are using these older designs without issue. Also, McDs themselves used these older machines without issue at the time.
The board members for McDs are also board members for the equipment oem, and the licensed repair orgs. It's about extracting money from franchisees more than it is about food safety. It could mean a reduction in maintenance and labor, but there's no reason that higher level store managers/assistants can't also be trained in basic maintenance on these newer machines.
If they're still the same machines from decades past when I worked at McDonald's then refilling the machine is just dumping a bag of mix in the container on the top. It doesn't take much qualifications. Slightly easier than refilling a printer.