anthropologically there are so many different types of marriage: Monogamous, polygamous, polyandrous, polyamorous, group, etc.

Cishet monogamous marriage, the type recognized as legitimate in the Capitalist West, the institution upholding bourgeois private property and family structures, will probably wither away under communism, but I doubt all recognized anthropological forms of romantic union will wither away. Our definition of what marriage precisely means is often limited.