The antonyms for the phrase "gone pieces" would be something intact or complete. The opposite of broken pieces could be whole, connected, unharmed, or undamaged. A few examples of antonyms can be a complete item, solid structure, or anything that hasn't suffered any damage.
For instance, if you have a glass that has gone into pieces, the antonym would be the glass that is whole, perfect, and unbroken. Similarly, if a building has gone into pieces, the antonym would be a building that is standing upright, solid, and intact.
In conclusion, antonyms for the phrase "gone pieces" are whole, undamaged, unbroken, complete, and perfect, among others.