In essence, in the immediate aftermath of the bourgeois revolutions of England and France, lord and serf were simply replaced by capitalist and labourer. Often to a point where they became indistinguishable. Sure, in a capitalist society, compared to a feudal society, your ownership of production matter more to circumstance than to nobility.
Or at least, that's the sales pitch.
So if democracy keeps capitalism artificially alive, is capitalism doing the same to democracy? That's harder to answer. But if capitalists keep on automating their production to the point where there are no labourers left, then who is to pay for the products they produce?
Marx and Engel may believe that capitalists were creating the very force to bring them down, but they may not be the labourers, but rather the robots with which they replaced the labourers.