The image is by Luca Bonatti.
I think the mystery of the entwives is such a poignant thing. The idea that every ent’s death means the entire species is one step closer to oblivion. The idea that the ents are just lonely all the time because they’re missing their loved ones.
It is pretty funny the way Treebeard just says they lost them and cannot find them. One theory is that the moving elm tree that Sam heard about in The Shire could have been an entwife. But, it seems more likely to me that it’s an Ent that was looking for the entwives. Who knows, there’s always hope.
One great thing about Tolkien is that he just doesn’t answer questions like this. I think he always talked about them like he had theories about them, but he didn’t really know. So, there’s no “word of god” about what happened to them.
We know 3 of the Istari and only Gandalf kept on task. Saruman turned evil and Radagast just did his own thing. So, they probably set up shop somewhere and tended oliphants or something. It’s possible they turned evil, but I don’t think so given that we never hear about them. If they turned evil I’d assume they would have shown up during the attack on Minas Tirith.
If I had to bet, I’d say they were killed by the easterlings and Eru was so disappointed in their performance that he didn’t bother returning them.