After the second temple was destroyed what happened to the keilim? When was the last time they were recordedly seen and where do historians or other academics believe they are today?
If you visit the Arch of Titus in Rome, there, on the arch, is a depiction of the Romans hauling off the treasures of the Temple, including the menorah. The gemara at Me'ilah 17b says that Rabbi Elazar ben Rabbi Yossi as having visited Rome and saying, "I saw the parochet [curtain to the Holy of Holies] of the Bais Hamikdash in Rome and there were some drops of blood on it” (indicating that they were the blood stains put their by the High Priest during the Yom Kippur service). He visited Rome with the famous sage Rabbi Shimon bar Yochai. The two of them had earned the visit because they saved the emperor's daughter from an attack by a demon.
In Mishna Avosk, perek 41, Rabbi Nasan reports that in addition to the parochet, Rome still possessed the Kohen Gadol's headband, the menorah, the table, and the vessels in which the incense was mixed.
Some 30 years ago I recall an article in Commentary that said that the Vatican had sealed off some of Rome's catacombs and the author suggested that they could still be in possession of some of the sacred items of the Temple. There was months of letters debating that point thereafter.