user11520: During this CCC conference from 2011, starting from 00:18:55, the presenter suggests that as bitcoins can be lost (lost private key, dead owner, sending to an "eater" address that nobody possesses, etc.), and as the total amount of bitcoins has a known threshold (21 millions), there is a possibility that given enough time, most bitcoins, if not all, will actually vanish (be unusable).
The questions is when?
Actually, according to him:

if 0.5% of bitcoins are getting lost per year, "all" bitcoins will be gone by approx. 2032;
if the losing rate is 0.1% per year, it will probably last for a century, but will ultimately be doomed.

And if we suppose that inactive wallets (2 years with no transaction) are in fact lost wallets, we reach that 0.1%/year threshold...

user11189: There is currently a bounty offered on BitcoinTalk for implementing a method that would add bitcoins back to the mining reward in the case that an address had no activity for over 50 years which would completely resolve this concern.
The post can be found here and is located at #3 on the list https://bitcointalk.org/index.php?topic=371601.0

user5406: Are you suggesting that 0.5% relative to the still available bitcoins are lost every year or 0.5% of the absolute amount of bitcoins? Anyway, either my math is lying or each would turn out to be about 10% loss in 20 years, which doesn't translate to "all" in my opinion.
Additionally, should the value of Bitcoin sufficiently increase (which would happen if as many Bitcoins were lost as you suggest), the protocol could be hard-forked to allow for another eight digits divisibility. While the distribution would remain the same, a fraction of a bitcoin would then still be enough to fuel a global economy. 
Finally, since this question was first asked, wallets with deterministic key derivation have become more commonplace. As it is sufficient to transfer the master seed for such wallets, it is almost trivial to bequeath such wallets.

user85: The math is clearly absurdly unrealistic because as there are fewer Bitcoins available, it becomes harder to lose them. So the rate of loss has to decay as the availability of Bitcoins goes down.

11520: <p>During <a href="http://media.ccc.de/browse/congress/2011/28c3-4746-en-bitcoin_an_analysis.html" rel="nofollow noreferrer">this CCC conference</a> from 2011, starting from 00:18:55, the presenter suggests that as bitcoins can be lost (lost private key, dead owner, sending to an &quot;eater&quot; address that nobody possesses, etc.), and as the total amount of bitcoins has a known threshold (21 millions), <strong>there is a possibility that given enough time, most bitcoins, if not all, will actually vanish</strong> (be unusable).</p>
<p>The questions is <strong>when</strong>?</p>
<p>Actually, according to him:</p>
<ul>
<li>if 0.5% of bitcoins are getting lost per year, &quot;all&quot; bitcoins will be gone by approx. 2032;</li>
<li>if the losing rate is 0.1% per year, it will probably last for a century, but will ultimately be doomed.</li>
</ul>
<p>And if we <em>suppose</em> that inactive wallets (2 years with no transaction) are in fact lost wallets, we reach that 0.1%/year threshold...</p>
 11189: <p>There is currently a bounty offered on BitcoinTalk for implementing a method that would add bitcoins back to the mining reward in the case that an address had no activity for over 50 years which would completely resolve this concern.</p>

<p>The post can be found here and is located at #3 on the list <a href="https://bitcointalk.org/index.php?topic=371601.0" rel="nofollow">https://bitcointalk.org/index.php?topic=371601.0</a></p>
 5406: <p>Are you suggesting that 0.5% relative to the still available bitcoins are lost every year or 0.5% of the absolute amount of bitcoins? Anyway, either my math is lying or each would turn out to be about 10% loss in 20 years, which doesn't translate to "all" in my opinion.</p>

<p>Additionally, should the value of Bitcoin sufficiently increase (which would happen if as many Bitcoins were lost as you suggest), the protocol could be hard-forked to allow for another eight digits divisibility. While the distribution would remain the same, a fraction of a bitcoin would then still be enough to fuel a global economy. </p>

<p>Finally, since this question was first asked, wallets with deterministic key derivation have become more commonplace. As it is sufficient to transfer the master seed for such wallets, it is almost trivial to bequeath such wallets.</p>
 85: <p>The math is clearly absurdly unrealistic because as there are fewer Bitcoins available, it becomes harder to lose them. So the rate of loss has to decay as the availability of Bitcoins goes down.</p>
