Nobody replaces one system with another, they simply occur from the ashes. You don't get to pick and choose. Certainly, we don't.
The most important point, though, is that capitalism can only fail. It's ecologically, materially and energy illiterate - it makes no sense. It's simply a question of when. It's a parasitic system* which, once it kills its host, will die.
Therefore, the question of what replaces capitalism is open to everyone, including those who deny that it's a parasitic system, against all evidence. What would you replace capitalism with? Or, if you prefer, how do you think capitalism evolves in a world with a dwindling resource base and limits to growth? Or, probably a better question (for all), is what do you see coming after capitalism whether we like it or not?
*As is socialism, and all forms of communism that have existed alongside other systems.