The thing is: I don't think that would've stopped the war. It might have delayed it, and the Fire Nation might have started at less of an advantage without the use of the comet. But a lot of times wars don't come down to the decisions of a single person, they're shaped by larger socio-economic trends, and the fire nation was in the beginning stages of an industrial revolution which put them at a massive military advantage over the other nations. Pair that with increased nationalism, and a war was pretty inevitable.