Who was the last person to be alive in the reichstag in world war 2?

I am going to assume you mean the Bunker where Hitler killed himself in the last days of the war. The last person alive in the bunker was Johannes Hentschel, the engineer, who stayed to keep the generator running for the hospital on the surface. He was taken into custody by the Russians, and imprisoned for about four years, and then lived quietly in West Germany until his death in 1982. Rochus Misch, the radio operator, was the other person left alive in the Bunker at the end, but he attempted to escape, being caught almost immediately on the street above by the Russians. Misch is still alive, but terminally ill. He is the last living person to have known Hitler personally. But when the Russians entered the bunker, Hentschel was the only living person there.