Yes, Fleance, the son of Banquo is able to flee to safety, thereby fulfilling the prophecy of the three witches and spoiling Macbeth's plan. But if you recall in Act I, scene iii, when the witches "hail Macbeth that shalt be King hereafter," Banquo asks them
If you can look into the seeds of time
And say which will grow and which will not,
Speak then to me, who neither beg nor fear
Their response is that he will be
Lesser than Macbeth, and greater.
Not so happy, yet much happier.
Thou shalt get kings, though thou be none.
These are the prophecies, or fates if you will , of Macbeth and Banquo, so you see Macbeth's plan fails because it is fate. Yes, Macbeth attempts to alter fate, and finds out that he cannot.