point of no return

noun2

1. •
   The point in an aircraft's flight when there is insufficient fuel to reverse direction and return to the place of origin.
2. •
   (figurative) The point in any process or sequence of events where some development becomes inevitable.

   • After Munich it became daily more evident that Hitler had passed the point of no return. With every burst of news from Europe the inevitability of war became more certain. — 1959