LinusR wrote: ... But maybe you should take some comfort from the fact that he is still active, doing something he enjoys, and he seems to continue his social life that is possible with a bike. ...
I think this goes to the heart of it. He faces imminent reductions in his independence and while that may make him somehow safer, it will do nothing for his happiness and general well-being. I went through something a bit like this with my late mother although, fortunately, she only ever went roaming once and immediately approached somebody - a true goody - who took her back into her flat, saw my name on the speed dial and rang me. So, I never needed tracking devices. My efforts were directed to things like TV remotes (and phones with speed dial buttons.).
She remained physically fit and independent to age 94 and died after a few months in a home. It's a cliché but you are doing what he would have wanted, had he known in the past how this would develop. All sorts may "go wrong" as this gets worse but IMO you are right to try to maintain this rider's independence for as long as possible and I hope somebody comes up with the goods re the tracker.