If one wants do go really deep and allow for distributed parallel offline work followed by merge (very much like Git for software versioning) then the things discussed in e.g. Exploring the Use of openEHR for Integrating Patient Health Records Across Multiple Systems - #8 by erik.sundvall could be of interest.
(I have been thinking of similar problems regarding disaster resilience but have not had time to go into depth.)
The design behind Applying representational state transfer (REST) architecture to archetype-based electronic health record systems | BMC Medical Informatics and Decision Making | Full Text (that has inspired part of the openEHR REST specs) also was intended to be easily represented in a file system hierarchy. Such a file hierarchy would make it easy to implement something that allows carrying along a number of EHRs - but one would need to cosider security implications of course.