Unless the 144,000 were raptured to Heaven, how could they appear before the throne of God? And they sung as it were a new song before the throne, and before the four beasts, and the elders: and no man could learn that song but the hundred and forty and four thousand, which were redeemed from the earth. (Rev 14:3)
When the tribulation is finished, they will be called to Mt. Zion here on earth, not in heaven. Mt. Zion is the name of the highest mountain on which the city of Jerusalem was built, it's the place David took possession of and transferred his court from Hebron. It is also called the "Holy hill." That's where Jesus going to gather his 144,000.