We bought the 414 from someone who was more or less such a man. He had 6 airplanes (including the 414). Over 90, had cancer, no medical, and really shouldn't fly anyway. He knew he had to sell them and he started the process of doing so, but it took a while and he wasn't in a huge hurry, despite having not much time left. In the end, he sold two - the 414 and a Baron - but the remaining (3 V-tail Bonanzas and a 421) did not sell prior to his death.
I think in most cases you're absolutely right - they feel that selling the plane would be like giving up on life. They want the hope that one day they'll fly it again, even though deep down they probably know otherwise. In the case of the 414, I think Mr. Rule (the gentleman who we purchased the plane from) died a happier man for having watched the 414 fly away to its new home, and knowing that it would fly again. He died a month or so after we took delivery.