Who, in addition to the Principal Investigator, should have access to research data, codes, etc. in case the PI becomes unavailable for some reason?

As a matter of good administrative practice, Principal Investigators should take steps to assure that there are means for others to access research data if the PI becomes unavailable.  This might mean sharing access codes, instructions or other means of access with collaborators, assistants or a departmental administrator.

See also: Data Retention