As the Lord did with Egypt (Jeremiah 46:26) and Moab (Jeremiah 48:47), there is also a promise of restoration for Ammon at some undefined time in the future. This is another example of the restoration the Lord will bring, not just to the people of Israel, but the whole world, through his Messiah.
6 “But afterward I will restore the fortunes of the Ammonites, declares the LORD.”