The French had three years to wipe out the Viet Minh before the Chinese Communists arrived on the Chinese-Vietnamese border and failed to do so. So I am skeptical of the argument that they could have done so if the Chinese Civil War had turned out otherwise. (Of course failing to wipe out the Vett Minh does not mean necessarily mean actually losing the war.)
The French were actually fairly successful before 1949. They restored their control of southern Vietnam in 1946. By the end of the year, they had retaken Hanoi and Haiphong. By 1947, the Vietnamese Communists were driven into the jungle. They survived, but really lacked any power to drive out the French. While the French weren't successful in wiping them out, the French were adapting their tactics. In a famous incident in October 1947, French paratroopers almost captured Ho Chi Minh and Vo Ngyuen Giap.
In general, France achieved many tactical successes in 1947-1948. They just failed in achieving a strategic success. However, that only meant the Vietnamese Communists could prolong the war. They had no ability to win until China fell to the Communists, and Mao could give them lots of support.
At that point the Communists could begin to put real pressure on the French and build up their forces.
IOTL, stalemate favored the Communists because it meant long term they could build up their forces. ITTL, the same stalemate actually favor the non-Communists because it means they can build up their forces.
Without a patron to support them directly, I don't think the Vietnamese Communists will be any more successful than the Malaysian Communists were. They could very well survive in the jungle and inaccessible parts, but they won't be able to control any sizable territory and certainly nothing important.
France also realized that old style colonialism was no longer possible, and accepted that some form of independence had to be granted. They were willing to work with non-Communist nationalists by 1948 as long as they agreed to work within a French framework and accommodate certain French interests. (that the US was prepared to only provide aid if some form of independence was granted was also a factor).
In a scenario where the Vietnamese Communists lack a patron, then inevitably the Vietnamese nationalists are going to win since they do have patrons (France and later the US) and control of the most economically productive regions. As they establish real independence from the French and built their own army, more of the Vietnamese supporters will defect from the Communists to the government, as they aren't ideologically driven.
Of course, knowing that China would not become Communist probably changes some of the tactics of Ho and Giap. It's entirely possible they will reach some kind of accommodation with the State of Vietnam and emphasize their nationalism.
To win, the French don't need to wipe out the Communists. They just need a stable State of Vietnam that can slowly deprive the Communists of its support in the rural areas.
It is not impossible for the Communists to win ITTL, but highly unlikely.