2. John the Baptist came in the spirit and power of Elijah, but he was NOT a reincarnation of Elijah. Indeed he plainly declared that he was NOT Elijah.
And they asked him, What then? Art thou Elias? [Elijah] And he saith, I am not. Art thou that prophet? [Christ] And he answered, No. (John 1:21).
3. Elijah MUST return to earth before the Day of the LORD (which is the Great Tribulation).
Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD: And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse. (Malachi 4:5,6)