It would appear that Microsoft Onenote vanished from the Australian Mac App Store today. My reasoning is thus: Yesterday I updated the app on my MacBook Air. Today there's no such update available on the iMac. Clicking on the updated item on the MBA shows this message: "Item not available. The item you've requested is not currently available in the Australian Store."
Further checking of MAS in UK & USA (using the excellent fnd.io) also shows up nothing.