I've expressed in the past my view that The Church isn't on The Earth during The Millennium. We're in New Jerusalem, which is also Yahweh-Shammah.
The physical city of New Jerusalem already exists, it's in Heaven, maybe it's accurate to say in a sense it IS Heaven. It is the Heavenly Zion of Hebrews 12:22.
The term "Sides of The North" appears in The Bible twice. Once dealing with Lucifer's Fall in Isaiah 14, and once in Psalm 48 talking about the Heavenly Zion when it descends as New Jerusalem.
It is my belief that the 144,000 are part of the Church and in some sense represent The Church.
Revelation 14 describes them as standing on Mount Sion. In terminology that implies now they have been Resurrected.
I see The Rapture in the Seventh Trumpet (which extends into the opening part of Revelation 12).
Revelation 14 depicts the Raptured Church standing in the Heavenly Zion.