Quick answer
The liar's testimony dies with him. The second line is difficult, and it probably contrasts a witness who actually heard something with one who did not.
Read both lines
The first line repeats chapter 19's verdict almost exactly, using the same verb that closed 19:9. The second is harder, because "the man who hears" can mean the man who listened to the false witness or the man who heard the events themselves, and "speak endlessly" is literally speaks forever or to the end. The most defensible reading takes the two as opposed witnesses: the one with nothing behind his words is silenced, and the one who was actually there can go on speaking because there is more to say. Testimony that rests on something outlasts testimony that does not.
Related: Proverbs 19:5 · Proverbs 19:9 · Proverbs 19:28 · Proverbs 14:25
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.