There's really quite a lot of old fashioned thinking on this thread. Having a BMI of 40 is really nothing very unusual these days - it's interesting how on many other threads the overwhelming opinion is that doctors are all backwards for even referring to BMI because it's not a terribly helpful tool, and yet here so many people are saying that a BMI of 40 (without any other information) makes GA dangerous!
The risks of surgery with obesity are of perioperative morbidity and mortality not just to do with the anaesthetic and TBH, it these days it'll take a lot more than a BMI of 40 to make an anaesthetist nervous! Any risk of surgery has to be balanced against the risks of other management options or of not doing anything. Clearly if someone is bleeding heavily enough to be needing blood transfusions (with the associated risk of transfusion reactions, etc) and there are no other appropriate management options/other options have failed, then the balance of risk/benefit would be in favour of doing a hysterectomy. The 'waiting list for a hysterectomy' is irrelevant here because it's a relative emergency. A spinal anaesthetic may be an option for a vaginal hysterectomy if the surgeon thinks that's a sensible option.
The risk of periop m&M increases if obesity is associated with other problems, like diabetes, sleep apnoea, heart problems, but even then in the scenario of uncontrolled bleeding the benefit may out weigh the risk.
The risk:benefit balance may also be different for different operations in the same person, so using the example PP sited above of someone having an emergency hysterectomy whilst obese then being declined a hernia repair may make sense - an elective hernia repair is more likely to fail/become infected with associated obesity (and I'm not sure I'd have been keen on the same person who'd declined to do it in the NH doing it in the private!).
While the economic implications of different options aren't usually the primary motivation behind decision making, it is also worth thinking about how the cost that someone having repeated admission for transfusions etc while they spend a year trying to lose weight might rack up, vs having a single admission for an operation that may fix the problem completely....