His girlfriend does not sound like the kind of person who would file a final tax return.
You can file as personal representative without being appointed, although that would help. Without a will that would be a somewhat tedious process.
If there was a will, an executor was named.
As representative you have to collect his financial statements and settle his affairs. Do you want to do that?
If there were tax deferred accounts (IRA for example), and he put her as beneficiary, there's nothing you can do about it.
