How would the Italians get to a landlocked colony, even if they wanted it? According to this
BBC Country Profile, oil wasn't discovered in Southern Sudan until 1978. Before then this area only would've been useful as a way to connect Egypt-Sudan with other colonies for London's Cape to Cairo railway plans.
There's very gain from controlling this territory other than keeping it out of someone else's hands or connecting a set of other colonies.
The '50s and '60s is also way too late in the twentieth century for haggling over colonial territories, and most forms of colonial rule itself to still be acceptable.
This is based on a somewhat constructivist view of international relations, but by then any colonial powers that still existed would be evolving towards loose confederations with a unified identity, like Portuguese Lusotropicalism, a series of ex-British colonies that are commonwealth members or have the Queen as head of state. Without WW2 Libya would probably cease to be a colony and be converted into an integral part of Italy as much as Sardinia and Calabria are.