If I understand @CreamyCookie correctly, he is not looking for auto save function but rather wants a "hot exit" feature (and I would like that too).
Hot exit is a feature of some modern editors that preserves unsaved files on quit without prompting the user to save them before quitting. A nicer explanation can be seen here: https://github.com/Microsoft/vscode/issues/101#issue-117679274
I searched in every plugin I could get, but I couldn't find such feature.