It really depends on several factors. Firstly how "strong" the colonial power is economically and militarily and how repressive they are willing to be in repressing revolts. On the even of the first World War, most of the colonial powers were increasingly democratising and public opinion might become wary of a long drawn out conflict. But it is possible that one or more of the colonial powers becomes an authoritarian dictatorship and is willing to mercilessly suppress opposition.
Before World War I there were notable revolts against imperial rule, among them being the Indian Mutiny in 1857. The Boer War was interesting because it aroused sympathy, particularly in the Netherlands and Germany for the Boers. There was also sympathy for the Cubans in the Cuban War of Independence from 1895 to 1898 in the United States. However, before World War I there and even thereafter there seemed to be little sympathy for revolts amongst non-whites or at least non-Christians. So while outrage against supression of the Irish, Boers and even Cubans existed, the Herero people who had revolted against the Germans in Southwest Africa were described in the 1908 Catholic Encyclopedia (published in Ohio) in the following terms "boastful, vain, avaricious, beggarly, given to lying and cheating, dishonest, and cruel and ferocious in their hatred" essentially justifying a genocide. Event King Leopold II's actions in the Congo Free State did not lead to any international sanctions.
During the interwar period, Ghandi's non-violence inspired many as he became a celebrity of sorts in the UK, something that would have certainly not happened in Mussolini's Italy had one of the Senussi leaders attempted a similar policy of passive resistance.
At that time, however, most countries respected the principle of Westphalian sovereignty. Each government was allowed to deal with their subjects as they saw fit, and even Nazi Germany never faced any serious international repercussions until 1939. Often when there was anti-colonial opinion in mother countries it was not so much concerned with the fate of colonial subjects as much as with the financial burden along with the physical burden of providing troops to defend the colonial empire. In France for instance opposition to the Rif War by the Communist Party began in 1925 because of what was perceived as what they they saw as "large masses of French workers and peasants, dragged despite themselves into a dangerous war to support capitalism".
After the war, the atrocities of Nazi Germany made it so that in principle at least the rights of human equality were enrishned in the international order. It was no longer possible to justify perpetual colonial rule on the basis that some races were uncivilised and Britain and Belgium at least began to make plans to develop and prepare their territories for eventual independence. The French and Portuguese planned to integrate their territories into a larger national unit. The French tried this with the French Union though the war in Indochina and the withdrawl from Morocco and Tunisia in 1956 along with the beginning of the Algerian War in 1954 put severe strains on the Union.
The Algerian War of Independence was unique insofar as Algeria had been an integral part of France when the first rebellion occurred in 1954. The FLN was supported by Egypt and later Tunisia and Morocco along with the Soviet bloc. Looking at public opinion in Metropolitan France it is interesting to see how quickly opinion turned from opposing independence to favouring independence for Algeria. In July of 1957, an IFOP poll found only 18% of Metropolitan French inquired supported independence for Algeria, but 53% favoured negotiations with FLN, hoping for a ceasefire. By August of 1958, the number favouring independence jumped to 41% and by February of 1959 to 51%, meaning that in less than two years the the opinion swung wildly. While in May of 1959, a poll found that 71% favoured a ceasefire and talks with the FLN. By that period most French were opposed to increased taxes to pay for a war in Algeria and sending conscripts there to defend the territory.
In Portugal which was a dictatorship, the government was able to resist the "winds of change" for a longer period. However, Portugal was by far the weakest and poorest of the colonial powers and had a metropolitan population smaller than all of the other colonial powers, meaning that it had fewer resources to draw on. In 1961 when the first revolt occurred in Angola it was said that most still supported defending the territory and according to one historian public opinion against the wars only soured beginning in 1966. From the onset, Portugal was faced with a UN arms embargo and except light arms and munitions was unable to manufacture any. It was able to procure arms from West Germany because the latter was not a UN member state and not subject to the sanctions with France often assisting, but these were often inadequate and antiquated. With rebels being supplied by the Soviet Union and its allies, the Portuguese government faced several challenges, with the guerrilla war in Portuguese Guinea being the most costly in men and arms. Importantly, international opinion began to condemn white rule in southern Africa, with the Scandinavian nations being openly hostile to the Portuguese, South Africans and Rhodesians, with the Swedish government calling for international boycotts and arms embargos.
If a regime like that of Fascist Italy managed to survive the war (through neutrality perhaps) the country would enjoyed several benefits lacking in Portugal. Firstly having a large armaments industry, and secondly, a much larger metropolitan population to draw soldiers and settlers. If Arab nationalism takes root, they are likely to cooperate with the French in Algeria and prop up the Egyptian monarchy to stomp out Pan-Arab nationalism. Fascist Italy would likely employ far more draconian repressive measures than the Portuguese could ever have afforded financially or politically. Italian policies in Libya might resemble those of the Soviets in Central Asia or the Chinese in Tibet and Turkestan, meaning that they could have swamped the area with settlers and marginalised the indigenous population. In Ethiopia, there was already resistance to Italian colonial rule, and the Viceroy there was assassinated in 1937. Large-scale repression probably becomes the norm, but the Italians are also likely to stir ethnic rivalries in the territory fomenting rivalries between Tigray and Amhara people and also supporting Oromo separatism along with supporting the Somalis and Eritreans. The Italians after their conquest of Ethiopia had made the Ogaden region part of the Somalia province along with granting the Tigray region to Eritrea.
To say that colonial rule could not last indefinitely is ignoring the the Soviet and Chinese policies towards subjugated peoples. It shows what is possible if a powerful colonial power wants to enforce its rule at all costs by utilising repression and brutality against those willing to rebel against central authority. One could even make the argument that the Israeli government could be extreme example of what a nation state is able to do to enforce its rule over subject peoples.
