One thing that probably has not been thought of, during the creation of BTC, is that the number of Bitcoins will be slowly reducing to zero. There will be, in some time, 21KK BTC, but what about bitcoin that get lost? I mean hardware malfunctions. Wrong address transfers. Lost passwords. Forgotten wallets etc.
Do we know, how many of all Bitcoins is in circulations at this moment? I mean we can count the number that indicates how many it should be. We however do not know how many of them is inaccessible.
One day it might be a problem, but probably not the problem of our generation. Still statistically that says bitcoin cannot survive.
Bitcoin is highly divisible, so if there is demand for Bitcoin, the price will just keep growing. Even if 20,999,999 BTC were lost forever, that remaining BTC will be enough, just make it more divisible (extend amount of divisibility more than 8 decimal places). Price would be insane for 1 BTC but the system would still work.
It's very unprovable that so many coins get lost but you are right, if time is infinite and supply is limited, at some point supply will be 0 theoretically.
It will probably take 1000 years for this being a problem so this is something future generations must have to deal with.