Can Law Enforcement demand Email companies to give them full access to a "deleted" email address?

They can demand whatever and the laws in the jurisdiction changes how easy or what they can demand. It seems likely that in the US, with a court order or under the FISA loophole, that Google would give up whatever data they have. You only asked about the law and in many jurisdictions the police are the law. I would assume any company gives ups all data they have. If a company doesn’t have the data than they can comply with the law without handing over data.