Log in to account.microsoft.com/devices or use the service order tracker with your order number. It often shows whether the keyboard is listed as “shipped,” “replaced,” “not repairable,” or still “in process.” Sometimes components are shipped separately, and the keyboard is simply on a different tracking number.
Look at the return paperwork. If the service order shows the keyboard as a separate line item, it should have its own status and tracking. If it’s missing from the return summary entirely, that points to it being lost or never processed at their end.
Contact Microsoft Support with the original service order number. Mention that both items were sent in together under the same warranty claim, only one was returned, and ask them to escalate to the service center to locate the keyboard or issue a replacement. Chat or phone tends to work better than email for this.