money which the bitcoin holders have put into the system, and expect to get back from it ---
I've put dollars into bitcoin but I don't expect to get back dollars. I expect to get back goods and services.
It does not matter. If you buy 1 BTC today, the only way you will get 240$ worth of goods tomorrow is if tomorrow's new investors, after buying all the 3600 coins that will be issued tomorrow, will
also buy from BitPay the 1 BTC that you spent on said goods.
Miners don't sell all 3600 coins. I don't sell the coins I mine (never have), along with many many many other miners.