1
general::
The place in a course of action beyond which reversal is not possible. For example, Once the contract is signed, we've reached the point of no return. This expression comes from aviation, where it signifies the point where an aircraft does not have enough fuel to return to the starting point. [c. 1940]
American Heritage Idioms
2
general::
Phrase(s): the point of no return
the halfway point; the point at which it is too late to turn back. (Often with past.) • The flight was past the point of no return, so we had to continue to our destination. • The entire project is past the point of no return; we will have to continue with it.
McGrawhill's American Idioms And Phrasal Verbs