I don't think surgeons are fongible assets. There is a lot of planning and study taking place before a complex operation. Not to mention most surgeons have specialties.
Surgeons are generally specialists in one particular area and possibly even specialists within that area (ie: only do knee replacements, etc.). Surgeons get better with experience, it's a skill, and different surgeries are different enough that experience doesn't transfer too much. There's also changes over time in best practices so skills degrade not just due to lack of recent experience. If I remember the best predictor of the outcome of your surgery is how many similar surgeries the doctor does per year.
My gut instinct is that this is incorrect, too, but I don't know enough about surgery to make a compelling argument.
I'd back myself to pick up Ruby (a language I've never touched before) and be productive, more than I'd trust a surgeon who only has experience with heart surgery to operate on my brain. Maybe that's ignorant of me.
I don't think that's the scenario @jrh206 was talking about, though. Most code written in Ruby doesn't have the sort of immediate risk to life or limb surgeries do.
For non-emergency surgeries it's often a long-term relationship where the same doctor who has seen the patient a few times would be the one operating - so if that particular surgeon isn't available for whatever reason, the planned operation would be rescheduled to a different date with the same doctor, not to a different doctor in the same day.