important native revolts against Ptolemaic rule, leaded by self-styled pharaohs : Herwennefer and Ankhmasis between -205 and -185 being the more successful contenders, taking the main part of Upper Egypt
The Hellenistic regime of the Lagids was military, organizationally and financially stronger than the Upper Egypt pharaohs.
So the only chance for them I see in
Antiochus III the Great returning from his Eastern campaigns when he smelled Egyptian internal trouble somewhere in 205-200; and returning for good with Grand Army.
As Antiochus III the Great had his hands full in the East he might get allied with the pharaoh of Upper Egypt against the Egyptian territories controlled by the Lagids; so the allies invade the Lagid territories, loot, plunder and take as much contribution as possible.
Antiochus would probably take Caele-Syria and the Mediterranean possessions of the Ptolemies; but he would keep the rump Lagid state in the Low Egypt as a counterbalance to the Upper Egypt.
So Antiochus III the Great is going far away east again and the Upper Egypt might have their chance against severely weakened and demoralized Low Egypt; if they play their cards well they can conquer all Egypt and unite it. If the non-Lagid Egypt doesn't threaten the Seleucids territories in Syria and in the Mediterranean, they might get away with it.
That would be "pure" Egypt without too many non-Egyptian territories; but when Antiochus III is defeated by the Romans, Egypt might take their chance and take Syria, the traditional sphere of influence of Egypt. Everything else depends on the character of the new native Egyptian regime - they might conquer as much as they want to the South of Egypt without disturbing their Mediterranean neighbors, especially Rome. They have free hands in the Red sea, Southern Arabia and African coast - that might become a nice Egyptian Empire, the Lagids were too preoccupied in the Mediterranean and neglected these definitely promising directions of expansion.
If new native Egypt is good in his conquests, strong financially, controlling Red sea and trade with India/Arabia, Egypt might become a force to be reckoned with. As opposed to the decadent Ptolemies, this Egypt would have much more recruiting pool - all ingenious Egyptians, not only 7% of "Hellenic population".
Together with Parthia Egypt might become a problem for Rome instead of an easy prey.