Riding safety with Alzheimer's?

In my volunteer work I sometimes deal with folks who have dementia, in this case Alzheimer's. Today we did a very long walk together. He is athletic and used to be a powerful high-mileage road bike rider so no problems in the power and endurance domain. The disease has progressed to the point where he would become disoriented on the roads or maybe ride into freeway onramps and such. So he needs a companion. No problem, that would be me. When I suggested that his (otherwise now quite passive) eyes began to gleam.
Like in this paper he has lost the ability to shift and since we live in the hills this means trucking our bikes into the flatlands where you can remains in the same gear the whole ride:
https://www.alzheimersresearchuk.org/news/cycling-dementia/
We would stick to bike paths, preferably ones with a low amount of traffic and definitely not many pedestrians. About 20mi from here we have an almost perfect one that is about 15mi long and has no posted speed limit:
https://www.usbr.gov/mp/ccao/images/fsc-new.jpg
I will also switch out his pedals from clip-in to flat MTB pedals, don't want to risk him not getting a foot out and fall (he is >70). I always carry a first aid kit.
My question is, what else should I prepare for? Searches on the web didn't reveal much, other than that cycling is beneficial in slowing the progress of such diseases.
We'll see how the first rides go. If very well then there will be other questions, such as whether there is a road bike bike with automatic transmission. Maybe based on Di2. They offer it but AFAIK only for electric MTB and maybe it can be adapted to non-electric road bikes:
https://velo.outsideonline.com/ebike/shimano-introduces-automatic-di2-shifting/
Of course, if the guy turns out to be a lot faster than I am and leaves me in the dust that could present a very different problem :-)
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Regards, Joerg
http://www.analogconsultants.com/