Pour out your unfailing love on those who love you;
    give justice to those with honest hearts.
11 Don’t let the proud trample me
    or the wicked push me around.
12 Look! Those who do evil have fallen!
    They are thrown down, never to rise again. NLT

I believe verse 12 is an example of what is known as ‘the prophetic perfect’.

”The prophetic perfect tense is a literary technique used in religious texts, most commonly in the Bible, that describes future events that are so certain to happen that they are referred to in the past tense as if they had already happened.” Wikipedia

David may have had certain specific people in mind who had fallen, never to rise again. But it is probably a more general statement about all unrepentant evil-doers. A day of Judgment is coming for them, and we can be so sure of this it can be described as if it had already happened.

”“Hallelujah! For our Lord God Almighty reigns.” (from Rev.19:6 NIV)