The Old Testament certainly shows that the sanctuary in the wilderness was patterned according to a heavenly model. Moses was not the originator of the tabernacle in the desert; rather, he built the sanctuary according to the pattern and the purpose of God (cf. Exod. 25:8; Lev. 20:3; Ps. 78:69).
Thus upon seeing the true one in heaven whether in vision or at the end, we would know what we were looking at, so having 24 elders here, made for recognition of those 24 elders in heaven, whether actual humans or not.
The things in heaven were already there when it was described to Moses.
The things on earth are patterned after things in heaven.
Thus -- the twenty four elders would have been in heaven from the beginning.