One thing I've realized about posting my musings about my "problem" on the internets is that it likely comes across that my life is in ruins because of the pain in my hands after long rides. Although my hands do hurt and I hope there's a resolution to that, there's an awful lot of ways to enjoy riding a bike without doing 1200K's. In fact, I rode 10K+ miles a year for more than 20 years before I did my first brevet.
At some point, my long distance riding will come to an end regardless. Right now, it's my hope that I've not yet reached that point and part of what I enjoy about doing longer rides is overcoming the hurdles they present. The problems with my hands is just one of them and I'm exploring different things to ameliorate the problem and writing about what I've tried and what I might try next, mostly for my own edification and to document for myself where I've been.
I've had conversations with other folks my age and older about when we'll stop doing the longer rides. The obvious answer is when we stop getting enjoyment out of doing them. Other answers are if we get a "career ending" injury. A bad crash might also bring about the end. Another answer (for me) is when I'm no longer fast enough to get adequate sleep. When I get to a point where I'm struggling to make control close times that's a clear signal that I'm done.
I'm not there yet and I'm still enjoying the challenge so I'll keep exploring alternatives that let me continue. If I don't find one, c'est la vie. I'll still ride my bike.