This is one prophecy that partly came true. Jeremiah (or someone who wrote the relevant prophecy) predicted that the original Ark of the Covenant would disappear and people would no longer think about it. That was a pretty big deal, since the Ark had traveled with the people, along with God's spirit, until its enshrinement in the Temple of Jerusalem:
And when you have multiplied and increased in the land, in those days, says the Lord, they shall no longer say, 'The ark of the covenant of the Lord.' It shall not come to mind, or be remembered, or missed; nor shall another one be made. At that time Jerusalem shall be called the throne of the Lord, and all nations shall gather to it, to the presence of the Lord in Jerusalem, and they shall no longer stubbornly follow their own evil will. (3:16-17)
We'd say yes to the first part of the prophecy, but no to the second. Most people don't really think about the original Ark anymore as an object of worship—except for Indiana Jones and his rival Nazi archaeologists, of course. And no one seems to know where it is, although the Ethiopian Church claims to possess it. Personally, we think it's in that warehouse at the end of the movie.
However, all synagogues have an "aron kodesh," a Holy Ark, where Torah scrolls are kept. These scrolls are the first five books of the Bible, which contain the instructions written on the tablets Moses brought down from Sinai—the supposed contents of the original Ark. These are the rules that the Judeans were constantly breaking and getting punished for as a result. And the ark is placed on the eastern side of the sanctuary (at least in the Western hemisphere), so Jews are always facing Jerusalem when they pray.
Whenever the Torah's brought out to be read, there are prayers describing what happened in Moses' day when the Ark was picked up to be moved or set back down when the Israelites went from place to place in the desert. So clearly, the Torah is a living embodiment of the lost Ark. There are references to the ancient Ark throughout Jewish liturgy, so we'd say that people didn't really forget about it. It's still a huge symbolic presence in Jewish worship even though the original is long gone.