There are different reasons on why people will stop buying bitcoin. Maybe BTC money is getting low or etc.
Perhaps when it comes to noobs. If we look at the majority of the people here with a decent functioning brain, they see a lower price as a major incentive to start accumulating. I have never done anything else than accumulating at the time the market tanks.
If the demand is getting lower, the bitcoin may end its' journey but I think this will never happen because every day, more people are joining here in bitcoin.
There is nothing wrong with a decreasing demand. It happens in basically each and every established market - there will always be periods of higher and lower demand, but that doesn't mean it's the "end" of a certain market. Bitcoin has gone through certain periods of time where the overall demand has decreased, where after that the market stagnated for quite a while. Did it harm Bitcoin? No. Just look at the exchange rate today. Difference with traditional (developed) markets is that they take years to recover from certain economical events that may lead to lower overall demand, where the crypto market moves over it in a matter of months, or even weeks.