Without Hernandez, the Patriots offense would be forced to play primarily from three receiver sets, and would lose a lot of their versatility and explosiveness. Nonetheless, we have a bit of good news, as Greg A. Bedard of the Boston Globe is reporting that Aaron Hernandez is expected back for Thursday's game against the Jets:
The Patriots should be able to get a stranglehold on the division with a victory against the Jets on Thursday. Aaron Hernandez (ankle) is expected back for that game. The Patriots held him out today because the short turnaround for Thursday probably wouldn’t have been possible.
Having Hernandez back should help absorb some of the impact of Gronkowski's loss as a receiver. Of course, Hernandez is a completely different player than Gronkowski and doesn't even play the same "position" really, but he will help add a dynamic option to the passing attack if he does return. The Patriots will still need to replace Gronkowski the blocker - and I'd expect Visanthe Shiancoe, Daniel Fells, and Michael Hoomanawanui to help there.