When a Jira team-managed project is deleted, all sprints that are active on it cannot be deleted nor can reports from them be viewed.

Steps to reproduce:

1. Create a new team-managed project
2. Create a sprint on the board and add issues.
3. Start the sprint.
4. Delete the board.

Expected behaviour

When a user attempts to delete a board, show a notification about the active sprints and let them choose to either complete or remove the sprints, or keep them active.

Actual Results

The board is deleted and after that the sprint is still accessible for most intents and purposes, but will return an error on different operations, for example It cannot be completed and report pages will be blank. Also, active sprints from deleted boards are still displayed in the 'Sprint' field suggestions too, which may be confusing for the users.

Workaround

1. Go to the Backlog of any Jira Software Company-Managed (Classic) scrum project.
2. The Backlog contains multiple swimlanes, the first ones are sprints swimlanes, the last one is the backlog swimlane.
3. Select an issue that is not associated with any sprint, an issue that is under the backlog swimlane.
4. Edit the issue sprint field and select the orphan sprint as your target sprint.
5. Now the orphan sprint is visible on the actual board, it should be a new swimlane inside the Backlog page.
6. Find the sprint you want to delete, and select ... > Delete sprint.

If the sprint is no longer needed, it is possible to delete the sprint:
https://developer.atlassian.com/cloud/jira/software/rest/api-group-sprint/#api-group-sprint