One idea I've had for this scenario is that
Operation Long Jump go ahead and succeed, killing the leaders of the allied powers. This has a number of effects on the subsequent leadership of the main allied powers which changes the dynamics of postwar diplomacy.
For the Soviets Molotov is killed alongside Stalin whilst Beria is blamed for dropping the ball on security and is quickly disposed. Soviet leadership falls into an uneasy duumvirate between Malenkov and Zhukov. Eventually Malenkov suffers an accident and Zhukov becomes the sole leader of the Soviet Union. Using his position as leader of the USSR, his position in the military and his popularity as a war hero he is able to launch a thoroughgoing and earlier Destalinisation program which goes a long way to improve the Soviet's image in the world (although Communist circles remain divided over fears of Bonapartism) and build a sense that Soviet leadership was entering a new era. His two main policy achievements involve removing most of the Stalinist old guard and replacing them with fresh blood and stronger ties and cooperation with the West. After securing the peace he retires from politics and lives out the rest of his days in peace, a Soviet Cincinnatus.
For the British both Churchill and Eden get killed and Stafford Cripps becomes PM (although Atlee might seem a more likely choice for successor Cripps was seen as a potential rival to Churchill, maybe throw in a successful
Cripps' Mission to give him more credibility and throw up some interesting butterflies in India). This leads to much closer ties between Britain and the USSR both during and after the war. In the 1945 election Labour wins an even bigger majority than IOTL, being able to leverage the prestige of Cripps as the wartime hero and the Conservatives being deprived of Churchill, which allows Labour to push through an even more radical program than IOTL. In 1950 Labour does better in the election and is able to win a workable majority. Cripps soon retires due to health reasons and Nye Bevan becomes PM, promising to continue Labour's policies of radical domestic reform and a foreign policy built on decolonisation and cooperation with the US and USSR.
For the Americans FDR gets killed and Henry Wallace becomes President. He was quite in favour of cooperating with the Soviets, a stance which Zhukov's Destalinisation will make a lot more palatable to the American people. He goes on to win the 1944 and 1948 elections, continuing his pro-cooperation foreign policy whilst pushing a left-wing economic policy and staunch support for Civil Rights. Amongst other things he extends Marshall Aid programs to the Soviet Union and the other Communist countries helping to economically integrate the US and Soviet Bloc and stabilise them. In 1952 the Republicans run Bob La Follette Jr. who wins and continues US cooperation with the Soviets and domestic Civil Rights reform. He is then re-elected in 1956. US-Soviet relations are now firmly entrenched and support for the alliance is bipartisan. There is no Red Scare, instead earlier and stronger support for Civil Rights inspires a violent right-wing backlash with rising acts of domestic terror and assassination plots against both Presidents and as a result the energy and resources that were used against Communists and their sympathisers is turned against them. It's not pretty but it does help pave the way for more effective Civil Rights.
Japan and Germany are both put under full joint-occupations with no separate occupation zones, which encourages greater cooperation between the occupying powers. Japan and Germany (including Austria) are reestablished as completely demilitarised and neutral republics.
In Italy, due to various butterflies and changes, the Popular Front are able to scrape a near majority and form a coalition with Liberal and Social Democrats. Italy develops into a 2.5 party system with Christian Democrats on the Right the Popular Front on the Left and Social Democratic Liberals playing kingmaker between them and wedded to a neutral foreign policy, effectively making Italy non-aligned. Combined with Germany this means that Soviet bloc and Western Europe now have two neutral buffer states between them, which helps keep tensions down.
With neither Britain or the US willing to prop up the Monarchists the Communists handily win the Greek Civil War. Increasingly surrounded Turkey is Finlandised and forced to give independence to Kurdistan.
Due to a more successful Cripps' Mission and with Cripps in charge of overseeing Indian independence things go differently. Partition is put off in favour of loose federation and a referendum on partition scheduled for a decade or so later. As a result Partition is avoided or is carried out in a more amicable manner and the subcontinent is much less of a hotspot as a result.
Because there is no Suez Crisis Nasser, whilst still quite popular, is not as entrenched as IOTL and eventually has to give way to democratic civilian government. The Arab world gradually unified into a Federal Republic as the gulf monarchies start to fall. The ethnic Kurdish regions are seceded to Kurdistan in exchange for aide from thee US and Soviet Union who are cooperating to ensure a peaceful and stable political order.
In the 60s a treaty is signed between Israel and the Arab Federation, overseen by the UN and with US-Soviet support, which establishes peaceful recognition, with Israel seceding the Negev to the Arab Federation, giving them territorial contiguity, in exchange for rights of access and transit to Red Sea ports and mutually beneficial trade agreements. To ensure that the peace is maintained large numbers of international peacekeepers are stationed in Israel. Whilst the peace doesn't please everyone it does manage to hold.
The French get pushed out of Indochina in the 50s and the whole region falls under the control of Communist-dominated Nationalist governments. They maintain open relations with the US who offers them aid and support.
When Fidel Castro overthrows Batista the US negotiates with him, meaning that he doesn't become a Soviet ally, which prevents fears of Soviet expansion into America's sphere of influence and the Cuban Missile Crisis.
Without Cold War fears of Soviet domination the Americans, along with the Soviets, back Patrice Lumumba and help him to stabilise the Republic of Congo. Whilst things aren't always smooth and there are a lot of problems things sort of work out in the end and Congo gradually integrates and unifies with the various Francophone African countries surrounding it.
Korea isn't partitioned and instead the Americans and Soviets backed the native Peoples Republic that initially declared independence. Postwar elections ensure that Korea is dominated by left-wing pro-Soviet parties and falls into the Soviet sphere of influence. There's no Korean War, Korea remains fairly open to the outside world and the madness of the Kim regime is butterflied away.
In China the Soviets and Americans desperately try to negotiate some sort of compromise between the Communists and KMT, however, Chaing and Mao proves to be too stubborn. So the Americans decide to cut Chaing loose and arrange an "accident" for him and replacing him with Yan Xishan. A power-sharing agreement is worked out and an uneasy triumvirate of Mao Zedong, Zhou Enlai and Yan Xishan is established. Mao is not particularly happy with this and there are right-wing KMT types who don't like the fact that they have been sidelined, so things aren't ideal, but they muddle through. With Mao unable to rise to total control in the 50s the worst excesses of the GLF are avoided with China focusing on more slow and steady economic plans. There are still problems, industrialising a country as large as China is never going to be a painless operation, but with more sensible economic targets and access to international aid and support it's a hell of a lot smoother than IOTL.
There is no space race. Instead there is international cooperation towards space exploration with the first moon landing completed by an international team.
By the time the 70s roll around rising economic prosperity, more openness and foreign influence leads to increasing demands for social and political reforms in the Soviet Union which results in the democratisation of the USSR and wider Communist Bloc. Peace reigns across the world under a broadly left-wing and democratic political consensus.