Well, he was probably at the extent of what he could do military wise. He had a empire and he needed to consolidate it. The Achaemenids really only truly solidified under the rule of Darius.
Alright, so, say Cyrus lives ten more years and finishes his conquest of Transoxiana, with the lands between the Oxus and Jaxartes rivers coming under Achaemenid rule. After this, he decides not to go to Egypt, but instead consolidating his empire, establishing a large part of the civil tolerance, the four capitals and consolidating Zoroastrianism and defining it to a further degree. This leaves an Achaemenid State which is more centralised since the beginning, probably more Persian (although I think the Akkadian, Aramaic and Elamite influence would still be there).
After his death in 520, Cambyses succeeds to the throne as Cambyses II, spends a few years devoted to the centralisation Cyrus started, and then launches off in the conquest of Egypt like in OTL. If this butterflies away the death of Bardiya, he succeeds to the throne, although maybe Cambyses has another son.