One word for the Point of No Return?

See Rubicon, defined by Oxford dictionary as

Point of no return.

But this term isn't that common. You may wanna use climacteric, critical point, etc. for different situations.

point of no return is a precise phrase with an arresting meaning: It

. . . comes from aviation, where it signifies the point where an aircraft does not have enough fuel to return to the starting point. [c. 1940 ] The American Heritage® Idioms Dictionary

You might consider crossroad or crossroads as a single word--one definition being:

A point at which a vital decision must be made. (source - dictionary.com)

How about brink? From Merriam-Webster:

1. edge, especially the edge at the top of a steep place
2. a bank, especially of a river
3. the point of onset, e.g. on the brink of war
4. the threshold of danger