The simple and obvious answer is that you draw the line wherever you think you should draw the line. That's what customer service is. Arguing that there is a slippery slope and therefore no accommodation should ever be granted is the the very definition of the complete absence of customer service.

Step back for even just one second and think about what you're really saying here. A guest of a hotel, engaging in the very activities that the hotel stay was purposefully booked for, had a daughter hospitalized with four vertebrae and your response is, "but it's a slippery slope". I own multiple businesses and I can't think of any circumstance where, if a customer/client called me and told me that he would be unable to satisfy some obligation because his daughter was in the hospital with four broken vertebrae, that I wouldn't want to be as accommodating as possible.

The hospitality industry is implicitly and primarily a customer service industry. If you want to learn more about the industry and the approach to customer service, a good starting point is introductory books like Solomon/Inghilleri's Exceptional Service, Exceptional Product or Michelli's The New Gold Standard or do a web search of the concepts within (e.g., both spend a lot of time on Ritz Carlton's 2000 rule).