If hpv can clear on its own is it possible it can come back without any sexual partners at all?

Yes: A "clear" hpv test may mean the virus is only 'suppressed' to sub clinical levels where it is not detectable and won't cause disease; but may replicate at a later time to detectable, clinical levels where it may cause changes. The further out a person is negative the less likely it is to become positive without new exposure, but it is possible.