This is a common irrational argument (meaning it requires more work to determine truth) regarding the exhaustion of "supply". A "coin" is simply a numeric value in a wallet of a whole amount. Fractional amounts can, and will, continue to be "created" using subdivision of existing coin. There is, with future code changes, no limit to the precision of the values stored there, so even a sub fraction of a bitcoin will still do to serve the entire network, if the network is still operating, of course.

The deflation issue is what is really addressed here, where no new coins will be introduced at a given point. Whether new coin arrives or not, is really not an issue. An analogy would be the use of pennies if all the paper money went missing.