ipad was set up with old deleted email account, how can I reactivate it?

You’ll have to try account recovery so you can use it again -> How to use account recovery when you can’t reset your Apple ID password - Apple Support

So what is the issue? You cannot get a 2FA code or something? Just because you stopped using, canceled or deleted an email services account doesn’t mean an AppleID does not remain an AppleID.

Once verified, an email address as the login ID for an AppleID continues to work just fine, regardless of what happens to that email address. So as long as you know the password you should be able to login. Unless that AppleID also uses 2FA and you have no trusted devices signed in with it so you can get a code?