Unfortunately, AFAIK, Azure DevOps does not have a Recycle Bin or native restore mechanism for deleted dashboards. When a dashboard is deleted, its layout, widgets, and specific configurations are removed from the user interface. However, you can investigate the deletion event to determine who deleted it and when, and explore alternative ways to recover the dashboard or minimize the impact of its loss. Btw. Microsoft does provide the option of recovering entire Azure DevOps org - but I gather this is not something you'd want to pursue in this case.
You can investigate the deletion through the Azure DevOps Audit Logs. Go to Organization Settings in the bottom-left corner of the Azure DevOps page, then select Auditing under the General section. Use the available filters to narrow the results by timeframe and search for dashboard-related events, such as Dashboard.Deleted or Delete. Locate the relevant entry to identify the user who performed the action, the date and exact timestamp, and any available details identifying the deleted dashboard. Note that auditing must have been enabled at the organization level for the event to be recorded, and audit logs are retained for 90 days. You can also download audit logs in JSON or CSV format or retrieve events programmatically through the Azure DevOps Audit REST API.
Because Azure DevOps does not provide a native undelete function for dashboards, recovery depends on the circumstances. If the dashboard disappeared because someone deleted the associated team rather than the dashboard itself, the dashboard might still exist in the backend as an orphaned resource. If you have its exact URL in your browser history, try navigating to it directly. If it loads, check whether you can access its settings and associate it with another or newly created team.
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hth
Marcin