Mining is the only process which can confirm your transaction when it is added in the block over the "block-chain" and thus the whole thing is working just fine becasue of them. So in any case if you think that supply is related to miners income source then that is completely wrong! Miners vital work is to confirm your transaction and complete the peer to peer process by helping the pools. Thus, though the supply dry out it has got nothing to do with it as we will still be sending the bitcoins to each other. Also, there is no relation of the coins which are not in the circulation as they are not moving anywhere. So its about the things (tokens/coins) that are moving in circulation.