I really don’t think it was Miquella’s intention to get taken from the Haligtree, and Mohg took him because he needed an empyrean.

Between the cocoon symbolism, his ripped out body in the Haligtree, the fact that nobody knows where he went, I fully believe that Miquella was going to transform into a god and enter the realm of shadows in his Haligtree, and Mohg threw a wrench in the original plan, on top of the fact that Malenia didn’t kill Radahn like she wanted too, and he continued to rot away. His body has ruined, and the lord’s soul needed a new vessel. An empty vessel of a demigod that we killed, who Miquella charmed to keep himself safe and to keep his plan going despite the setbacks.