As of now I have a non-existent phone number on WhatsApp. My tablet has been running really slow lately so I decided to factory reset it. I backed everything up with titanium backup and also backed up WhatsApp chats to Google drive. I really don't want to create a new WhatsApp account because I'll have to notify all my contacts etc. but as I don't have the phone number that I originally obtained my WhatsApp number anymore I wanted to know if there is a way to restore my WhatsApp account either from the drive backup or titanium backup? (Sorry for the illegibility I've been working on this problem the whole day)
You should be able to restore your account using titanium backup if you have app+data backup of whatsapp taken using titanium backup.
However, there can be cases of app crash, if the backup is corrupted, android version of your device upgraded/changed. Also there can be a scenario in recent/latest version of whatsapp where it would detect this dirty restore and ask you to authenticate the number again. If this happens try using a bit older version of whatsapp(you can download it here) as I recall I was able restore whatsapp account using titanium backup a couple of years back.