Sorry, my friend, Cartman DOES die! There's a scene where Kyle and Stan drive a stake in his chest and Kenny saws off Piggy's head just to make sure.

And the subplot with Liane trying to dispose of the body: burial is not an option becuase nobody wants to be his pallbearer and forklift rental was too much; cremation was taking several days and seniors were coming to the crematoruin, thinking they were smelling a Boston Market; a burial at sea was impossible because he kept bobbing back up to the surface; and donating him to medical science was impossible, since all the medical schools kept telling her that they only take HUMAN bodies.  So, she just hauls his carcass to Purina.

Let's not forget the touching scene where he's finally renuited in the tenth layer of hell with his mother, Ilse Koch.