There is no concept of "lost coins" per se, there are only coins not spent recently. You can't tell ultimately if someone is saving for their retirement or cannot spend the money.
In a macroeconomic scale, if money is removed from the economy, then that means the remaining currency must hold the value needed. For now, with Bitcoin, about $2M worth of Bitcoin is being printed every day, and I doubt it's being lost at that rate.
https://en.bitcoin.it/wiki/Myths#Lost_coins_can.27t_be_replaced_and_this_is_bad