It's a tricky question. On the one hand artists would have been acutely aware that their work could be destroyed as needed; buildings were after all often renovated(destroying any immobile works such as frescos) and artwork could be thrown out as it fell out of fashion. On the other hand, we do know of work to preserve and record artwork deemed historically significant. For instance, while much of Giotto's work for St. Peter's has been utterly destroyed by 16th and 17th century renovation work copies were made earlier of the famous Navicella mosaic and at least one fragment was deliberately preserved and recorded as such:

Giotto made the fresco of the Angel...and many other paintings, whereof part have been destroyed and part in founding the new walls, have been either destroyed or removed from the old edifice of S. Pietro, up to the space below the organ; such as a Madonna on a wall, which, to the end that it might not be thrown to the ground, was cut right out of the wall and made fast with beams and iron bars and thus removed, and afterwards built in, by reason of its beauty, in the place that pleased the pious love that is borne towards everything excellent in art by Messer Niccolò Acciaiuoli, doctor of Florence, who richly adorned this work of Giotto with stucco-work and also with modern paintings.

So we see here that some works could be deemed worthy of especial preservation and honor by virtue of their artistic merit. A similar project was undertaken even more remarkably on a work of Correggio, who worked within Vasari's lifetime:

...where he painted an Annunciation in fresco so well, that, when it became necessary to pull it down in making some changes in that building, those friars caused the wall round it to be bound with timber strengthened with iron, and, cutting it away little by little, they saved it; and it was built by them into a more secure place in the same convent.

So it was certainly possible that artists could expect their paintings to be preserved or maintained during and after their lifetimes but they could also expect that some artwork would be lost-and remember, during the Renaissance art was nearly always made for some specific purpose(as decoration for a chapel or palace, as an aid to devotion, as a means of commemorating or propagandizing a notable individual, or other purposes) and not independently created as an end unto itself.