WhatsApp chats disappeared after Android Operating System Update

I am having a Moto E XT-1022 (1st generation) 2014 model. In order to update its OS from 4.4.4 to 5.1, I had to make 500MB space available so I deleted all WhatsApp database backup files without copying them elsewhere as I knew from my own experience that WhatsApp had nothing to do with Android OS upgradation process since I had already upgraded the same android from OS 4.4 to 4.4.4 and my old Samsung even before that without losing any of my WhatsApp messages but unfortunately, this time all my chats are gone after OS update. As I thought, WhatsApp tried to take the backup automatically on 3 AM like any other day, but it's not working either. Now I'm left with a possibly corrupt file msgstore.db.cypt8 (size: 103.62 MB). I read somewhere in here that there is a possibility of mending the corrupt backup and regenerating it afresh if the key can be extracted somehow. So is there any ray of hope for me? PS: Mine is a non-rooted device.