Did Theseus die

In the case of Theseus of the Greek Legends, Theseus did die, but later life is rather enigmatic. After his son was killed by Poseidon's bull (or Dionsyus's bull in some stories) for supposedly raping Theseus's 2nd wife, his popularity declined.

Some say that after his decline of popularity he left towards Lycomedes of the island of Skyros, who pushed Theseus off a cliff to his death.

Overally, the theory that Theseus was pushed off a cliff is currently the only information regarding to Theseus's death.