If you do not have a Microsoft account with the key backed up, and the system is still bootable, see below.  If the system is no longer bootable and you have not backed up the key elsewhere, it's lost and the only way to return the system to operable status is to completely reinstall Windows. [URL]  
Hi there, Its been quite a difficult situation and that too with such a brand that i am trying to connect with the customer care,Dell service centers but not getting connected with anyone of those.  I am facing a technical issue that i am unable to get the recovery key for the key ID FF0E6CFA. Since, your customer care and service center failed to guide, i searched on Google and neither i have any microsoft account details to sign in and get these id's to proceed further. Request you to resolve the matter at priority. Regards, Abhinandan VRF Aircon Pvt Ltd
48 Digit recovery key not available for key ID FF0E6CFA