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I don't think the tresish ones were the Entwives or we'd probably have known that. The Entwives went to the Brown Lands and made gardens, between Emyn Muil and Mirkwood. The forces of Sauron drove them out. I personally feel that the forces of Sauron probably burnt them all or destroyed them as well. I don't think Sauron or his followers were really lovers of trees and nature much and just letting them go wouldn't satisfy him. So in my own opinion, they're extinct.
They could have wound up as kindling. Or the planks of an elvish ship, but since Radagast doesn't know or is unwilling to say; and the eagles, and Tommy isn't telling Gandalf..I think
They never left, but whenever they see an ent coming, they stand really still.
Look, Hal Sam's cousin claims he saw a "walking" tree. Treebeard said the Entwives would like the land of the Shire. Therefore it is entirely possible that some of the Entwives are up there, or it could just be an Ent. However, I think that if the Entwives were destroyed there wouldn't be any evidence, because they would just be burned.
And, there is nothing in the Lord of the Rings that suggests the location of the Entwives, whether literally or figuratively.