No Viewport when converted to DWGWhen converting a DGN to a DWG, and there is a reference from the design model into the sheet model, the reference disappears and no viewport is created.
The file does not have an active view open. When saving to DWG, with no active views, it will cause problems in the resulting DWG file, including not creating the expected viewport.
Open a view, Save Settings, and save the file. Then do the conversion, and the Viewport should be created properly.