I think “operating indefinitely” is a bit of an exaggeration. Proxy wars do eventually come to a conclusion, and the results can be dramatic. To your point, France backed the American War of Independence against the British, and once the American side won, the course of history was completely changed by the founding the United States. And the American insurgency in Afghanistan partly led to the collapse of the USSR, which also dramatically changed the global strategic chessboard. The level of proxy warfare in the world has clearly increased in the past few years, and the question is how will it end.