When it's dead, it's dead. But what I do is remove the container (some of them). Glue them on a masonite board which is my palette and create artwork out of them. No good to waste ...recycle. Of course, if you don't like the color ... cover them with different ones.
And it's such a pain in the *** because I have a bunch of paint myself that got packed away so I couldn't get to it and dried up. What a freaking waste v_v
Once it's dried, it's trash. There is no solvent, because when acrylic paint cures, it undergoes a chemical reaction and turns into a plastic polymer.
Trash it and buy fresh.