Question

Where did Medea escape to after her plot to kill Theseus was foiled?

Answer 1

According to Wikipedia...
Medea then returned to Colchis and, finding that Aeëtes had been deposed by his brother Perses, promptly killed her uncle, and restored the kingdom to her father. Herodotus reports another version, in which Medea and her son Medus fled from Athens on her flying chariot, to the Iranian plateau and lived among the Aryans, who then changed their name to the Medes.[13]
So she fled to the Iranian plateau.