What happens if the deposit was already released to the seller before the deal fell apart?

This turns entirely on why the deposit was released and what actually happened afterward. If the purchase agreement itself allowed early release once a specific milestone was met, and that milestone genuinely occurred, the release was proper — getting the deposit back after a later collapse then depends on what the agreement specifically says about deposit forfeiture or return in the circumstances that caused the deal to fall apart, not simply on the fact that the deal didn't ultimately close.

If the deposit was released without the conditions for release actually having been satisfied — for example, a lawyer released it in breach of the agreement's terms or an undertaking given to the other side — that's a more serious problem, potentially involving a separate professional-responsibility issue for whichever lawyer released it improperly, on top of the underlying dispute between buyer and seller. Review exactly what condition supposedly justified the release and whether it was genuinely met before assuming the release itself was proper or improper.