I am not sure that communism is on the right path to coexist with democracy right now, at the moment they both seem like total opposites of the coin. It is possible that some day things will change, the governments will define what democracy is and what communism is differently and they will coexist though.
First off, the idea that any two governments cannot exist in the same world is ridiculous. Besides that, communism is not the opposite of democracy (the US isn't even technically a democracy, it's a republic). It is however the opposite of capitalism, although that is not necessarily democracy. If there is a communist state that is run by elected officials, then by definition it is a communist democracy/republic. I believe there are socialist democracies in Europe that are quite successful, including Norway and Sweden (I think)
They are 2 completely different things. Someone prove me wrong but I can't see it. Communism can't coexist with democracy because we have been at war for so many years. We fought Castro and what good came from that? Nothing but death and destruction. I believe we will be at war with communism for as long as we exist.