A user story calls for an extension to a current feature. This is reviewed and discussed in planning and given a small/medium point value. Internally within the team the effort is estimated at 2 to 3 days. As work progresses it becomes clear that it is not possible to extend the feature in the desired way without significant effort - it calls for a re-architecture and near total rewrite of the feature so that it can be extended in the desired way. This is epic in size and could take 4 to 6 weeks of effort.
How should the scrum team handle this? Specifically;
- Should the original user story be removed as it cannot be completed?
- Should the sprint be backfilled to make up for it?
- Am I correct to add an epic to the backlog and link it to the original user story?
The story cannot be carried over, it is a dead duck. As far as I see it is up to the product owner to review the new epic and prioritise as appropriate. It may never even happen.