So poor little Monty isn't urinating? I'm surprised they think he will last a week. (I used to be an emergency room nurse. For humans, not cats. But kidneys are kidneys.)

Don't second-guess yourself. You did a good thing. He has food and water now, and he's warm. And he doesn't have to worry about being attacked. Although, I suppose, it's possible he perceives the humans around him now as potential attackers.