what kind of proof did they have to think that? Or do they just assume because he hasn't written anything since?
I think it is quite normal that he would stop writing.
I will look for a link. The article actually came out immediately after her death, kinda like it was well known in literary circles etc.
Whodunnit, Really? Is Dick Francis really the author of the novels that bear his name, or were they written by his late wife, Mary? Consider: He dropped out of school at age 15, whereas she had university degrees in French and English and once worked for a publisher. Prior to Mary’s death in 2000 (she died in his arms of a heart attack at age 76), Dick Francis produced a new novel every year. But after Mary died, he said that he doubted he would ever write anything longer than personal letters ever again. “So much of my work was her.” Indeed, for years Dick Francis credited Mary with an extensive role in the creation his novels, and he repeatedly urged her to accept credit as a co-author. She refused, arguing that “Dick Francis” was the brand name readers responded to. In the end, it hardly matters. But unless you have worked as a husband-and-wife writing team, you can’t really appreciate the melding of a genuine collaboration. And if you’re over 80 and have written a novel a year for more than the past 30 years, who can blame you for hanging up the racing silks?