Stalin lets Czechoslovakia keep Carpatho-Rus. Eventually the federalization of Czecholslovakia leads to it consisting of three republics--Czech, Slovak, and Carpatho-Rus--all of which become independent with the Velvet Divorce.
Some evidence that Stalin had not decided on making Carpatho-Rus part of the USSR until rather late: "No sooner did the Slovak revolt succumb to overwhelming German power than the Russians shocked Benes by demanding, albeit by proxy, cession of a portion of Czechoslovak territory. They were the force behind the mass rallies in the Carpathian Ukraine which from the end of October onwards began to clamor for its unification with the Soviet Ukraine. Radio Kiev seconded the demand, and the Red Army barred London's plenipotentiary from assuming his duties as stipulated by the Czechoslovak-Soviet administrative agreement of the previous May.
"The Soviet behavior was all the more disturbing since the Russians had until then recognized the province as an integral part of Czechoslovakia and had also made their Czechoslovak Communist lieutenants plan on that assumption. As late as October 26, the Soviet press had reported approvingly about the arrival of Benes' plenipotentiary in the Carpathian Ukraine, and the local Communist party boss, fresh on the scene from Moscow, had hailed the bright prospects of living in the same state with the Czechs and Slovaks.
"The Carpathian Ukraine, one of the most backward parts of Europe, was an economic liability to any owner, and Benes had not nurtured strong feelings about it. In 1939, he had told his confidants that it would be to Czechoslovakia's advantage to have the Russians there.” On several subsequent occasions, he had spoken to Majskij [the Soviet ambassador to Great Britain--DT] in the same vein. And during his Moscow visit in December, 1943, he had supposedly hinted to Stalin that the Soviet Union could have the area for the asking, but Stalin had shown no interest.
"The Russians considered the territory a potentially dangerous 'Piedmont' of Ukrainian separatism. Yet this alone would hardly explain the sudden reversal of their policy in October 1944. Their newly perceived need for a common border with Hungary after the unexpected pro-German coup there seems to have provided the impetus. And the near-certainty that the Benes government would not resist made it safe to proceed. By simultaneously raising doubts about the future of Slovakia, where several thousand additional Ukrainians lived, the Russians turned the screws on Benes, pressing also for Czechoslovak recognition of their puppet Lublin government of Poland.
"The Carpatho-Ukrainian affair was typical of Stalin's power diplomacy. After Benes had tried to temporize, the Soviet leader sent him an insidious letter recalling his earlier willingness to part with the territory, castigating the Czechoslovak government's presumed (though never actually stated) disapproval of the Soviet behavior there, and warning against any effort to interfere with the supposedly freely expressed will of the Ukrainian people. The result was not only Benes's obsequious protestation of good will but also a speedy recognition of Lublin by Czechoslovakia as the first country after the Soviet Union. The eventual cession of the Carpathian Ukraine was a foregone conclusion, and it was formalized soon after the end of the war..."
Vojtech Mastny, "The Czechoslovak Government-in-Exile During World War II."
https://www.jstor.org/stable/41046033
(The Czechoslovaks. with Soviet approval, attempt to allay any concerns about Carpatho-Rus becoming a hotbed of Ukrainian nationalism by teaching the Rusyns that they are not Ukrainians but Rusyns, with a language admittedly related to, but not identical with, Ukrainian. To be sure, some Rusyns may reject this, and after the breakup of Czechoslovakia urge unification with Ukraine. But remember: Moldova didn't unite with Romania.)
You might say that an independent Carpatho-Rus would be too small and poor to survive, but maybe it retains some sort of economic and military union with Slovakia, while keeping its sovereignty and language.