Vázquez says Durandus meant only habitual grace
Vázquez does maintain that Durandus is speaking there not of any grace at all but only of habitual and justifying grace. He does not think any Catholic doctor has taught that man can resist every temptation against natural law, and so keep the whole natural law, not only for a short time but for a long time too, without any help of grace through Christ.
When Durandus and the other older Schoolmen debate the overcoming of temptations and the keeping of the natural precepts, and ask whether a man can overcome all temptations and keep all the precepts without grace, by 'grace' they mean, he says, not the help of moving grace but habitual grace, by which we are righteous. On the Prima Secundae, vol. 2, disputation 189, chapter 2.
Latin
XII. Pertendit quidem Vasques Durandum ibi loqui, non de gratia quavis, sed solum de gratia habituali & justificante; & non putat aliquem esse Doctorem Catholicum qui docuerit hominem posse evitare omnem tentationem contra jus naturale, ac proinde servare omnem naturalem legem, non solum brevi, sed etiam longo tempore, sine ullo auxilio gratiae per Christum. Durandum enim & alios veteres Scholasticos, quum disputant de victoria tentationum, & de observatione praeceptorum naturalium, An sine gratia possit quis vincere omnes tentationes, & observare omnia praecepta; per gratiam non intelligere auxilium gratiae moventis, sed gratiam habitualem, qua justi sumus. In primam 2. tom. 2. Disput. 189. cap. 2.