I have to say, looking at that schedule, it doesn't look too bad. Especially when you take into account that West End performers routinely do 8 shows per week with two performances on matinee days - and their contracts are often for 12 months. By contrast, MJ's 50 shows would have been split into two halves with several months break inbetween and no back-to-back shows or travel to different venues. Still a lot of shows, but a schedule that should have been within his capabilites.
If you are a professional entertainer then I wouldn't have thought that schedule was too tough.