Sure, the attempt to keep those colonies did eventually spark a revolution in Portugal, but Portugal was able to keep them for decades after our WW2 and the de-colonialism it spurred.
TTL's Italy might fare better for longer than people can imagine
I agree completely.
Let's suppose that Italy stays neutral during WW2. The outcome of the war would pretty much be similar to OTL. In the following cold war, Italy would be too important to control the mediterrean to be ignored or marginalized. To secure Mussolini collaboration, USA would have to turn a blind eye to the colonies problem. To paraphrase Kennedy, Mussoloni would be "a mean bastard, but our bastard".
Now, the subsaharian colonies would be impossible to keep, since the great disparity between the local population and the colonial one. Maybe through USA mediation they could reach independance without too much bloodshed (or maybe provoke the fall of fascim as happened in OTL Portugal).
Lybia is a different kettle since the italian element could become the majority of the population. In such a situation the fascist regime could even hold a "free plebiscite" among the population to let them decide if becoming independent or stay part of Italy. Besides fighting rebels in the desert would be easy for italians, since they enjoyed total air superiority and could control all the water sources.
The nail in arab coffin would be the italianization, with forced settlements, schooling in italian language and an assimilation of the ruling arab elites.
As for the local politic, Italy could probably attract Egypt into her orbit, but even if Nasser manages to get to power this won't automatically spell the end for italian rule in Lybia. On contrary I always had the strong impression that a fascist Italy would have partecipated to the Suez Crisis and in the end would have become the best ally in Europe for Israel. An alliance between the two would alter considerably several of the wars in the Middle East