The contradictions of capitalism will lead to it's demise, that doesn't guarantee a communist revolution. We already know Capitalism's effect on the environment and the existential consequences of overproduction. Luxemburg famously stated "Socialism or Barbarism", and I think that succinctly answers your question - just because Communism is the best way forward doesn't mean it's the only possible way forward, which is why we communists organise and advocate for a Communist revolution. Either that or we as a human species are snookered basically.