It's really only a matter of time before the Achaemenids conquer Egypt in its current state. Time after time, when the Persians were pushed out by a revolt or native pretender, they simply came back with more men and brought the Nile Valley back under control. However, if Egypt can consolidate after the victory at Pelusium and wrest control of the Levant from the Persians, they would be able to recover the international power and prestige of the New Kingdom. There's no way to know what would happen afterwards due to massive butterflies, as the entire dynamic of the Near East is changed. There are no Greco-Persian Wars, no Peloponnesian War, no rise of Macedon or Alexander, and there is no gurantee that Rome comes to dominate Italy at the expense of the Samnites and Greeks.