Reality:
1. Probably more than half of the hospitals will have a critical system fail after an earthquake. Just because it doesn't fall down doesn't make it usable. Chances are that it will take significant time to get them working again (hours, days,weeks) after something major (5+ under or 6+ nearby). The nature of the beast is complexity coupled with errors made all throughout the process from construction through maintainence up to the day of the event. Welds and bolts will break. Electrical, plumbing and sewage lines (let alone oxygen lines) will fail. The list goes on.
2. Utility service will be disrupted, with water systems damaged and/or contaminated after an event. Try living for a week with all of your utilities (water, gas, electric), and see how it works. Most aren't prepared. Ask the hospital people just how long their generators will run. The answer may just surprise you. And is there an on-site water supply? If so, how big, and how many gallons per person does that actually accomodate?

I'd go on, but the fact is that during the lighter ones, everything should ride it out (up to about a 4-5- appx 30-50 miles away). Above 5, I'd look for significant disruption. Perhaps temporarily (same day), but there will be a significant number of systems that will be out for weeks to months. Whether these systems are critical enough to make a facility unusable can only be assessed after the event.
Before I hop off my soapbox, remember this:
Most of the controls systems are made overseas, and subject to just in time delivery. Generally, there aren't huge warehouses back east filled to the gills. If transportation is disrupted, so is the flow of parts.
Gasoline is pumped by electricity. No juice, no gas. From the distributor that fills the tankers, to the corner gas station, electricity is required.
The saddest commentary I had with a manager was a critical facility that had a 24 hour rated fuel tank (only enough fuel for 24 hours). I had the audacity to ask, "What happens if we have an EQ and the power is down as long as it was after Northridge?"
The response: We have a contract with a vendor to deliver a truck load of fuel for the generators.
Hope they get there before the gennies shut down...