What if Ho Chi Minh had died during WWII?

Yangon Agreement, 1974

The leaders of Burma, CPV and China gather once more, this time on the Burmese city of Yangon, May 1st 1974. The CPV, whose envoy was Giap himself, wanted to expand westwards, and bring several areas in Southeast Asia - mainly the Spratly Islands and possibly Sarawak - under a united Vietnamese Federation. China was mostly in favor of Giap, since a win for the Vietnamese was a win for China, given the protectorate status under which Giap was constrained. However, Burma was dissatisfied. He though he was being left out from the lot. General Ne Win - leader of Burma - was afraid that, after the war, Burma would be either annexed into China or emerge dangerously unfavored, or at least, the Burmese wouldn't be rewarded like Vietnam and China. The General demanded that China should give up all land west of the Mekong River all the way to Burma's northernmost point, from which place a straight line will be drawn up to the river to create a western border. This displeased the Chinese, who needed Burma's strategic location yet were unwilling to sacrifice territory. This ploy was made by General Win in order to not only create a buffer zone but also to force some kind of benefit regardless of the war's final agreement. The CPV strongly opposed Burma's stance and influenced China to not to fall into Win's "trickeries". China refused to make concessions, although promised to pay Burma over 500m dollars to cover mobilization costs. Win instantly agreed. After many days of deliberation, a series of accords were created, giving birth to the Yangon Agreement. It stated the following:

a) A hardline Communist regime will be installed in neutral Cambodia and Laos, following an invasion of said countries.
b) Cambodia will be placed under the CPV's zone of influence, while Laos will be divided between China and Burma. Burma will receive all areas in the south of Laos (giving Burma a border with the CPV) while China will obtain the north. China agrees to create northern Laos a protectorate Communist regime.
c) Thailand will be transformed into a Communist puppet regime under the trilateral influence of the Hanoi Block. 
d) Malaysia will be transformed into a Communist puppet regime under the trilateral influence of the Hanoi Block. 
e) The Hanoi Block agrees to collectively leave 500,000 troops in continental Southeast Asia.
f) Under any circumstances, the US will not be provoked into war at all costs.
g) The conflict must be swift and end with an agreeable peace treaty that leaves Britain content. She must be immediately pushed out of the continent, capturing prisoners rather than massacring them, and forcing massive evacuations. 
h) Hong Kong will be immediately captured. 

The Hanoi Block agrees on a combined strategy: The Burmese and Chinese fleets will blockade the Gulf of Thailand, cutting off Thailand's supplies. If Britain does not give up immediately, the Vietnamese will launch a sudden invasion of Cambodia, while Laos is blockaded and a land invasion of Bangkok from southern Burma will be executed. All military efforts will be supplied by China. As Britain's forces are tied south, China will invade Hong Kong. Once Britain is expelled, they will push for a peace treaty that Britain will find impossible to refuse. As the meeting was over, Burma became increasingly wary. Such an operation will soak the main bulk of Burma's military, leaving her northern border exposed. She feared China would break her promise, or that everything already was a conspiracy ploy to trick Burma into a dummy war to leave their guard down. As Win put it: "Since when did the Cat help the Mouse, if not to eat it later on?"

Allow me to answer your doubts.

Not much has changed with the Sino-American relation. Nixon sees an untapped treasure trove in mainland China and is certainly handing security council status to Mao. Taiwan will be pissed, and as such will be declaring neutrality, believing itself to be short of allies, especially after British companies in America see interest in the new opening of relations. 

Britain, with Nixon's political and moral backing, has decided to ship vast amounts of soldiers into Thailand and Malaysia mostly as a facade. They want to make the Chinese believe they have a strong presence in the region, sort of like a: "You mess with me, and you're gonna suffer. Look how many troops I've got!" Obviously, the British propaganda machine has grossly exaggerated the UK's strength. Most natively-British troops are either untrained reserves or part of volunteer corps. The main infantry role was taken by Thai and Malaysian conscripts and personnel. You have hundreds of thousands of poorly-armed, untrained, unmotivated farmers forced to fight in some random war they heard about just days prior, quite literally doing the rich white man's bidding. Add in the tiny fraction of outside troops from S. Korea, Australia and such, which are able to provide a high amount of troops, since the OTL Vietnam War didn't happen. That being said, the British are in no position whatsoever to wage real war, and will soon be overpowered by the Hanoi Block if hostilities erupted. As soon as Thailand comes is overrun and Hong Kong is lost, the Britain will sue for peace, something the Chinese also want. It would end up being a real embarrassment for the UK, possibly even causing PM Harold Wilson's resignation (although highly unlikely, given he had become PM just months earlier). Have in consideration that Wilson was highly moderate on socialism and would've avoided true war at all costs. 

So anyways, for the main question, that's the deal: most soldiers weren't proper British troops but rather Thai and Malaysian peasants. The UK seeks to avoid war at all costs, while the Hanoi Block seeks a swift and limited offensive that leaves high gains. 

That's the thing! If China sweeps across SE Asia, it means some really wacky things will end up happening. The way I see it, it leaves room for a lot of revolts, uprisings and revolutions. 

The Malayan Peninsula will serve as an impregnable stronghold for the Allies. Indeed, the Malayan Peninsula will be impossible to be captured by the Chinese, and it would be incredibly difficult to fully occupy. The region will harbor the fiercest resistance against any kind of Communist regime, if not a full-out secessionist movement. 

Yeah, but reversed. The Communists would find it impossible to properly occupy the region, giving rise to a free Malayan republic. The Allies would recognize this revolutionary state as the true government of Malaya and give aid to the insurgent movement. It is possible that, with the gradual degradation of Communism, this revolutionary entity may take over as the sovereign state of Malaysia, although most likely the Peninsular portion of it.