Bitcoins lost is lost forever, irreplaceable, and unrecoverable.
Lost Bitcoin not having a "heartbeat", or I think the correct analogy is not having a "crash cart" to bring it back to life, or circulation, never to be available to be mined, is a good intended feature.
It just makes the Bitcoin's you're holding now much more valuable!!! Scarcity is great feature!
Remember this factoid. Bitcoins total mined is around 21 million, but even though there's a cap on total number of Bitcoins to be mined, doesn't mean there's a finite amount of Bitcoin. Bitcoin is divisible by 8 places, so in reality, there's a near infinite amount of Bitcoin that can be used by the masses...