Your firearm is your private property. As long as you have the legal right to posses it... The police can NOT take it permenantly. However as long as it holds some criminal evidentiary value it may be held. A person who is no true billed, or cleared by a coronors jury should get his property back forthwith. Local jurisdictions may have some rules allowing them to hold on to the property for a period of time... In one jurisdiction the firearm may end up being destroyed before it can be returned. That same jurisdiction will usually remove any permission to posses the firearm (Revoke the permit) A person could make a civil case I guess.
While IMO you will probably get the gun back, but it may be marked by the vouchering officer, and may not have been stored well or taken care of.