Ask Lemmygrad

It won't. What it will do is allow successful revolutions to have a large trade partner to help develop their country. But China isn't in the business of spreading revolution or defending allies like the USSR was. If Cuba got invaded by the US tomorrow I highly doubt China would do much more than try and coordinate with the UN to stop it or something. Perhaps they may secretly fund Cuba or whatever but again, I doubt anything directly. Not hating on China or anything. Its perfectly reasonable to look out for yourself first as a country. Even if it seems a bit, nationalist (because it is), its a reasonable approach.