I think perhaps, after her voyage(you know when she was on a ship at the end), she returned to Underland. She did say she'd "be back before you know it" to the Hatter so I think it would be nice if she went back and saw them all(especially the Hatter) again.

I think, she went to China, to finish her business. And when she finished it, she returned to Underland, since she promised to Tarrant, she'll be back. I don't think, she broke her promise.

I think she finished the trading in china, then came back to england to marry some dude. then had a few kids, one of which followed the white rabbit into wonderland and became next in line to the white queen's throne.

In a story I made I had her marry a man named William who was friends with my character, when they were expecting their first child they met Zutara (my character) who was getting married to the Hatter thus after their adventure Alice and William had their first daughter and went to live in Underland. Where Alice and Zutara are the champions and work in the court as well.

I think as the others said, she went on her voyage, and was successful with trading with China. Then I think she returned to Underland and stayed there permanently. I personally think it'd be awesome to see her and the Hatter get back together and maybe even marry! They're obviously perfect for each other, and Tarrant was heart-broken when she left. So anyways, I think she'd return to Underland, marry Tarrant, and live happily ever after.