QI-Core does not include a profile for TaskNotDone as it does for other resources. For specific instances such as medication reconciliation or medication review, QI-Core recommends use of Task but without a clear reference to how to address TaskNotDone. Suggestion:

Modeling for TaskNotDone should be similar to the way the other QI-Core "notDone" profiles are constructed, requiring a status using the Resource's status value set if an appropriate value exists, a statusReason, a code for what wasn't done, a timing (for Task, I believe Task.authoredOn is appropriate since Task.period is about the time the task actually happened), and reference to the encounter and patient for whom the task is intended. So this may be helpful for modeling in the absence of a specific FHIR a TaskNotDone profile:

• Task.authoredOn for the dateTime - the timing the task was rejected and the reason.
  Task.status.status with valueset-task-status constrained to task-status-rejected (The potential performer who claimed ownership of the task has decided not to execute it prior to performing any action.)
• Task.statusReason binding to Negation Reason Codes (extensible)
• Task.code:code (Codes to identify what the task involves. These will typically be specific to a particular workflow.) For a direct reference code, it needs a cardinality of 1..1 and binding to the code use indicate for medication review or medication reconciliation. If the measure requires a value set, it would need a Task.code:code.coding.valueset-reference URL: http://hl7.org/fhir/StructureDefinition/valueset-reference to reference the value set not performed - similar to the mapping for ProcedureNotPerformed
• Task.encounter (Healthcare event during which this task originated)
• Task.for (Beneficiary of the Task) Reference (qicore-patient)
  Consider guidance or addition of a new TaskNotDone profile for QI-Core