The after 1950 stipulation is interesting, and somewhat limiting, but I'll give it a try.
The Communist side agrees to an armistice in Korea by April-ish 1951, after the front-line has stabilized above Seoul and roughly along the 38th parallel.
The PRC makes a diplomatic campaign after the armistice in spring and summer of '51 of demanding withdrawal of the US 7th fleet from the Taiwan straits, and redistributes troop resources towards the southeast coast.
The US of course digs in on preventing a Communist takeover of Taiwan, and Mao gets increasingly pissed off.
Without the active war in Korea, the PRC has also massively stepped up aid and advice to the Viet Minh from May 1950 onward. The US likewise is stepping up aid to the French in Indochina.
To get back at the west for obstructing his goals, Mao and Ho and Giap agree that in addition to arming up larger Viet Minh forces with more firepower, China will send a massive expedition of "Volunteers" into Indochina to tip the scales in the battle for Tonkin.
The plan is to employ the Viet Minh and Chinese volunteers in a two month campaign supported with a major artillery park to breach the De Lattre line, defeat the French and sweep away French control from Hanoi, Haiphong and the whole Red River Delta. After this, the Chinese volunteers are to withdraw and the expansion of Viet Minh forces is to continue.
Attacking in Tet 1952, the Communist forces achieve operational level surprise and overwhelm French forces, killing many, forcing some to disorderly retreats to the sea, and bagging several thousand prisoners from French forces.
Since the majority of French forces are in the north, this severely depletes them. Viet Minh economy of force operations also tighten the ring around French positions in central Annamese cities like Hue and Da Nang, and expand in the southern Vietnamese countryside. Meanwhile other detachments of Viet Minh, Chinese volunteers and local "Pathet Lao" do a big push to sweep away French posts in northern Laos occupying and raiding towns and posts as far south as the Mekong on and the northern Thai border. Then they do a big recruitment drive to enlarge the Pathet Lao.
The French of course start sending reinforcements, and the Americans stage in Far East Air Forces from Japan, the Philippines, Taiwan, carriers and Thailand to strike at Communist concentrations.
But, inside the 6 to 8 week period, the French are still crushed in Tonkin and the Viet Minh flag is raised in Hanoi and Haiphong, and the Chinese forces announce and begin to execute their retrograde back north to China, with alot of PoWs in tow.
The Americans are grimly prepared to make a major effort with the French certainly thinking about sending a significant ground force. The Truman administration is also trolling for third country allied support and not finding the British and others receptive. The Americans are also demanding political concessions by the French to Indochinese independence.
From Paris, despite the rage at the sneak attack and desire to avenge their defeats in Tonkin, a variety of pressures converge to make for a bleak assessment. With sufficient support, the French and their allies can land in and seize Haiphong and drive back to Hanoi, but it will be a tough campaign with the Viet Minh occupying a bunch of of urban and rural fortifications with alot of captured French kit and local pro-French sympathizer and intelligence networks smashed. So it's hard. Plus, French public opinion is very concerned about getting the PoWs back, and the Communist side exploits on film and radio PoW forced "confessions" of evil-doing. Finally, with all the demands from the Americans for sweeping reform and Indochinese independence, the French government starts to wonder what it's all for.
So instead, in spring 1952, the French agrees to Communist offers to negotiate an end to the war and return of PoWs.
After dragging on for a few months, the Communists and French come to an agreement the Americans hate. The French get their PoWs back, a Viet Minh and Communist evacuation from Cambodia and Laos, pledges of political representation and amnesty or freedom of emigration for non-communist/anti-communist Vietnamese, but in return there is a caretaker provisional coalition government established to govern all of Vietnam with the Viet Minh or their fronts monopolizing military and security posts, set up to conduct national elections in December 1952, and a full French military withdrawal from their remaining positions in central and southern Vietnam after the vote count.
The Viet Minh and front organizations win the elections and the French evacuate in the early months of the Eisenhower administration, even as the Americans have been objecting and protesting the whole time.
...so there's that...
I welcome other solutions to the challenge. This one required alot of contriving.