If we spend our money the total mined Bitcoins number won't go down. No matter how much and if we do or do not spend, Bitcoin's total mined number will just keep rising. This is why there is a halving of the block reward every four years: so that it'll take a LOT of years (maybe it'll become even impossible?) for us to reach the 21MBTC mined. We have approached it but it's not going to happen too soon - it'll take some time to mine a few more millions because now the block reward has been halved to 12.5BTC.
and don't forget that the difficulty of bitcoin is always increase from time to time so the amount of bitcoin rewards that have been mining should be reduce more and more and without a big hashrate, we can not get big bitcoin in a days.
and for the holder, if they still want to hold their bitcoin, its mean the supply in the market will be reduce and its make a big demand on the market and its should make the price going to jump, but i think the price is being control by someone else behind all of this. and remember, i think satoshi itself is predict about this and i am sure that he is make calculation, so i think we don't have to worried about anything. and if something bad is really happen, then its our choice, want to stay with bitcoin or leave bitcoin to save our self.