Why? Many drivers started out in lower teams and then progressed to teams higher up the grid. Team bosses know how each car should classify and take that into account when evaluating a driver. Plus the fact that he is still a Ferrari-junior of course.
Heck, Leclerc started in Sauber himself. Russel in Williams, Vettel in Sauber, Alonso in Minardi, Kimi also in Sauber, Schumacher in Jordan. The examples are many...
Seriously, it would be a shame. If he is able to keep driving like he did for his one race with Ferrari he deserves a better chance then Hass will give him.