The best replacement for quantum theory is relativity.

The best alternatives to quantum theory are rated as following:
★★★★★  relativity
★★★★★  string theory
★★★  general relativity
★★★  classical theory
★★  theory of relativity
  bohr model
  wave theory

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Speaking about quantum theory, one probably shouldn't forget about general relativity.

Other search terms related to quantum theory and their ratings are:
★★★★★ general relativity
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quantum theory
relativity
string theory