2 answers, maybe even 3.
1. No, his presence is what is necessary, so why assume he will prophesy?
2. Sure -- as has been stated on another thread, those who had prophecy before the destruction of the temple will have it still
3. He is dead. What comes back is a spirit/angelic version which won't prophesy as a person but will speak on behalf of God as an angel.
Elijah must prophesy because his job is to announce the arrival of the Messiah. Simply standing around with a sign saying, I'm Elijah, is not enough.
In 2 Kings 2:15 it says, 'And when the sons of the prophets which
were to view at Jericho saw him, they said, The spirit of Elijah doth rest on Elisha. And they came to meet him, and bowed themselves to the ground before him.'
So Elijah will not be recognized by his name but by his spirit; which means that the message he delivers is all important. Moreover, we are told what that message will be.
Malachi 3:1, 'Behold, I will send my messenger, and he shall prepare the way before me:'
Isaiah 40:3, 'The voice of him that crieth in the wilderness, Prepare ye the way of the LORD, make straight in the desert a highway for our God.
[Now compare this with Mark 1:1-7, Matthew 3:1-6, if you'll allow yourself to study the New Testament.]
One further bit of information that you can confirm, or dismiss, is that the name Elisha means 'God has helped' and the name John means 'Yah has shown favour'. Remarkably similar, and possibly intentionally so, because Jesus says this,
'Verily I say unto you, Among them that are born of women there hath not risen a greater than John the Baptist: notwithstanding he that is least in the kingdom of heaven is greater than he.
And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take it by force.
For all the prophets and the law prophesied until John.
And if ye will receive
it, this is Elias, which was for to come.
He that hath ears to hear, let him hear.' [Matthew 11:11-15]