restore ipad air without icloud password
An ex employee has returned their iPad Air however has left it signed in to their iCloud account. This account was created using a work email address which is no longer active so I am unable to do a password reset via the forgotten password link. Is there a way that I can delete this account and restore the iPad back to factory settings to allow someone else to use? It has allowed me to update to iOS 8.1.3 and I have been able to successfully overwrite the old Apple ID in the app store (I tried it with my own). Any help would be gratefully received!
iPad Air, iOS 8.1.3