Post Sandy, at the NYU Medical Center, they recounted the problems associated with no access to EHR after their systems went down. Bad enough when they were still in their own hospital, but very serious when they transferred patients to other hospitals. The story is that staff physicians, nurses and residents went with patient cohorts to the receiving hospitals and served as verbal medical records to get their patients situated best.
Well crafted database and server replication might help in a scenario like this, but so much of the infrastructure in NYC was broken, I doubt it would have.
This is an IT problem but it also extends beyond that simple statement. It requires human factors, so that the medical personnel can use it readily. It requires that common conditions be addressed (e.g., in obstetrics, it should be able to calculate EDC from LMP and project a due-date). I'll accept having separate adult, pediatric and neonate elements to help with dose calculations; that's not too bad and almost everyone's smart-phone can do those calculations close to automagically now. It needs customizable checklists for common procedures, AND an ability to go outside the checklist for issues/complications. It needs a good problem list generator and then a tracking system to allow repeat visits to recognize a problem list entry and bring it up at the next visit... or for a home phone call sooner if need be.
And did I mention it needs a data exchange format that really works? Recent experience: I had to see someone in a new city for care. My primary care physician's clinic (using a large EMR system they're abandoning in favor of EPIC) printed and faxed the whole chart to the doc's office in the other city. And when I asked the doc to send stuff back to my PCP? Yep. They faxed it all back (save the important stuff which didn't get sent at all).
EMR's something I've loked at for over 20 years and played with off and on. I was playing with it when the best way to automate was to create a lab-reporting system using VAX PDP-8's and DECterminals. Expensive? Slow? Yes but with a little screen building and database work, it was useful. I've watched HL7 and its predecessors over the years and they continue to get more robust, so getting the infrastructure standards in place isn't too hard.
What's hard is getting the INDUSTRY to stop being greedy and decide to interoperate. And to respond to the primary users, who are the medical professionals who have to hammer on the damned systems daily.