I've long been a fan of the "All Creatures Great and Small" books, and loved the BBC series when it was on TV, too.
Recently I Netflixed the first disc of the first season, and may have to buy the entire season. It's every bit as charming as I remember. It's so lovely and slow-paced compared to most shows today, and really, I can almost get past the fact that every other scene features someone with his arm up a cow's bum.
After watching it, I looked up what happened to the three main vets--James Herriot, Siegfried Farnon and his brother Tristan Farnon.
James Herriot, the author, was really named Alf Wight. He died of prostate cancer in 1995, 3 years after being diagnosed. You can still tour his surgery in Thirsk, rural England, as well as tour sites from the TV series.
The quotes on his Wikipedia page are perfect, exactly as you want Herriot to be. According to Wikipedia, he said ""Years ago, farmers were uneducated and eccentric and said funny things, and we ourselves were comparatively uneducated. We had no antibiotics, few drugs. A lot of time was spent pouring things down cows' throats. The whole thing added up to a lot of laughs. There's more science now, but not so many laughs."
Tristan, really Brian Sinclair, is best remembered by many viewers because he was portrayed onscreen by Peter Davison, who later played one of the Doctors on Dr. Who. I love how, according to Wikipedia, the real Brian didn't mind being portrayed as a bit of a rascal, unlike his older brother, who was not a huge fan of how he appeared on screen.
But the one that gave me a lump in my throat was Donald Sinclair, the inspiration for Siegfried, Herriot's boss. He lost his wife of 50 years, his brother, and his partner Herriot/Wight, in a short period of time, and according to Wikipedia, took his own life by overdosing on barbituates.
It's weird to say this, but I was so touched by how he killed himself...I think he just thought "well, I've helped guide so many animals out of their suffering with a simple bit of medicine, and now I'm alone and hurting and all my friends have gone. Perhaps that's the way to end my own suffering as well, I'll just follow my animals."