Talking about miners; the duties of a miner is not limited to just mining. Yea they get rewards for mining, but there are other benefits they gain by sticking around performing other duties.
Every time we initiate transactions, miners validate those transactions and ensure no double-spending occurs. They still go ahead to add this transactions to a block and then add the block to the blockchain. The transactions fees we are charged goes to the miners. Our only concern should be that when all the bitcoins are mined and miners no longer get rewards, they might likely shift their attention to transactions fees and charge higher fees. We really shouldn't bother about this because we might not witness this period when there will no longer be bitcoins to mine.
Maybe by the time these unmined bitcoins will eventually be mined, this guys can change their names from miners to something else that suits the job they perform in the Bitcoin network, especially in ensuring decentralization goes smoothly.
I would assume the transaction fees will be enough for them to survive, not like they are only working for the mined ones right now anyways. But we need to figure out a way to make this better, to convince them, because they are not making much even now, but assume they do, they won't make much in the future at least.
So either price has to be insanely high, so that low amount of bitcoin be fine, or we need to figure out a way to pay them a lot while we pay less. maybe bigger blocks could be reason, that way, they get more, while we all collectively pay for it and not individually. In any case we need to figure out a way, maybe mine isn't great but we need to make sure that we find a way to pay them more some other way.