Yajuj and Majuj: Are They Alive?
Question

My question is regarding the tribes of Yajuj and Majuj. I understand that they are huge in number, are plunderers and are destined for hell fire.
My question is: do they still exist? If they do, are they confined within the wall erected by Dhul Qarnain? Is this wall (doorway) imaginary or physical (made of metal)?
Praise be to Allah.Who are Yajuj and Majuj?
There is no doubt that Yajuj and Majuj are two huge nations of the sons of Adam. Anyone who reads the story of Dhu’l-Qarnayn and how he dealt with this nation in Surat al-Kahf will know for sure that they exist and that the barrier which was built is not metaphorical or imaginary, but is a physical barrier built of iron and melted copper. 
The basic principle is that we should take this Quranic text as it is, without resorting to any kind of misinterpretation or trying to twist the intended meaning.
Wall of Dhu’l-Qarnayn: Real or imaginary?
The Quran has told us how the barrier was built and what materials were used, so it is not right to say that it is a metaphorical or imaginary barrier. In Surat al-Kahf, Allah has told us the story of the Muslim king and the great leader Dhu’l-Qarnayn (may Allah have mercy on him):
“Until, when he reached between two mountains, he found, before (near) them, a people who scarcely understood a word.
They said, ‘O Dhu’l-Qarnayn! Verily! Yajuj and Majuj are doing great mischief in the land. Shall we then pay you a tribute in order that you might erect a barrier between us and them?’
He said: ‘That (wealth, authority and power) in which my Lord has established me is better (than your tribute). So help me with strength (of men), I will erect between you and them a barrier.
Give me pieces (blocks) of iron,’ then, when he had filled up the gap between the two mountain-cliffs, he said, ‘Blow,’ till when he had made it (red as) fire, he said, ‘Bring me molten copper to pour over it.’
So they [Yajuj and Majuj ] were made powerless to scale it or dig through it.
(Dhu’l-Qarnayn) said: ‘This is a mercy from my Lord, but when the Promise of my Lord comes, He shall level it down to the ground. And the Promise of my Lord is ever true.’” [al-Kahf 18:93-98]
Hadiths about Yajuj and Majuj 
What indicates that these nations exist at present, and indeed are attempting on a daily basis to get out and attack people, is the hadith reported by Ibn Majah with a sahih isnad from Abu Hurayrah (may Allah be pleased with him), who said: “The Messenger of Allah (peace and blessings of Allah be upon him) said that Yajuj and Majuj are digging every day until they can almost see sunlight, then the one who is in charge of them says, “Go back, we will dig again tomorrow.” Then Allah restores (the barrier) and makes it stronger than it was. (This will continue) until the appointed time. When Allah wishes to send them against the people, they will dig until they can almost see sunlight, then the one who is in charge of them will say, “Go back, we will dig again tomorrow, in sha Allah.” This time he will say “in sha Allah”, so when they come back (the next day), they will find it as they left it, so they will dig their way out and emerge to attack the people. They will dry up water (by drinking it, because of their great numbers), and the people will seek to protect themselves from them in their fortresses. They will fire their arrows into the sky, and the arrows will come back down covered in blood (as a test for them), and they will say, “We have defeated the people of the earth and have gained the upper hand over the people of heaven.” Then Allah will send worms on the napes of their necks, which will kill them. The Messenger of Allah (peace and blessings of Allah be upon him) said: “By the One in Whose hand is my soul, the beasts of the earth will grow fat from their flesh.” (Sahih Ibn Majah, 3298)
Umm Habibah bint Abi Sufyan reported from Zaynab bint Jahsh (may Allah be pleased with them) that the Prophet (peace and blessings of Allah be upon him) entered upon her in an agitated state and said, “La ilaha ill-Allah, woe to the Arabs from an evil that has approached! Today a hole like this has been opened in the barrier of Yajuj and Majuj ,” and he made a circle with his thumb and forefinger. Zaynab bint Jahsh said: “I said, ‘O Messenger of Allah, will we be destroyed even though there are righteous people among us?’ He said, ‘Yes, if evil becomes overwhelming.’” (Reported by al-Bukhari, 3097).
And Allah knows best.