the bitcoin will be found again after a few 100 years.
Technically, this is correct. It might not even take that long. That is, as soon as Shor's algorithm is actually implemented, Bitcoin is no longer secure. But of course, that is a much bigger issue and not really related to this discussion.
To answer OP; lost coins/keys will cause deflation, which is good for people who already have bitcoins saved. Because bitcoins can be divided to very small denominations, there will probably never be an issue of too few coins.