I agree with Angela.

The correct phrase is "**the point of no return**". While you might occasionally see "a point of no return" used, it's not grammatically incorrect, but it's less common and doesn't convey the same meaning. "The point of no return" refers to a *specific*, singular, and well-defined moment or stage in a process or situation. It implies there's only one such point. Using "a point of no return" would suggest there are multiple such points, which doesn't usually fit the intended meaning.