Maybe it will be mined for some reasons that there could be some losses on the supply definitely the team could add some more coins on it knowingly that there could be a percentage of the losses of that crypto. There could be a substitution to it as we all know that even in fiat money where the physical money is being lost and damaged it will be replaced by other physical money. The team knows how to calculate for it so we will going to trust them.
how does one tell between coins that are lost vs coins that have simply never been moved by the owner?
if bitcoin ever adds to the 21 million supply (for whatever reason) then it would be an alt, not bitcoin.
We are still a few hundred light years away from that (figuratively speaking), so if we continue mining at the same pace, it is definitely not our concern. On the flip side though, we don't have to wait until the 22nd century when we can break outside 21M coins to witness Bitcoin turning into
a pumpkin an altcoin. All we need to do is to change its protocol and start mining a little faster, and voila, Bitcoin is no longer what it used to be. In fact, it has already been done (and probably not just once). The result is Litecoin, a Bitcoin copycat.