Estius' answer: Adam's immortality was in one way natural, in another above nature
To make the view of the Roman school's teachers on this question clearer, I think it worth setting out what William Estius teaches on it, very precisely and clearly, in his commentary on the second book of the Sentences, distinction 19, number 9.
There he answers the question "Whether the immortality of the first state was natural to man" with many different distinctions. He teaches that it was natural to man in one respect and above nature in another, just as death is natural to fallen man in one respect and against nature in another.
Latin
XIII. Ut autem distinctius intelligatur quae sit de hac quaestione Doctorum Scholae Romanae sententia, visum est hic referre quae ea de re accurate & perspicue admodum tradit Gul. Estius in secundum sententiarum Distinctione 19. num. 9. Ibi enim ad quaestionem, Utrum immortalitas primi status fuerit homini naturalis, per multas & varias distinctiones Respondet. Et docet eam illi quadam ratione naturalem, & quadam ratione supra naturam fuisse; sicut & mors homini lapso quadam ratione naturalis est, quadam ratione contra naturam.