Bitcoin has a limit to the number of tokens it will release. That number is hard-coded at 21 million. The estimated date of Bitcoin issuing its last coin is believed to be in the year 2140. No one can predict what will happen at that point, but miners will always earn some profit from transaction fees. Plus, users of the blockchain and the Bitcoins themselves will be incentivized to protect the network, because if mining stops, Bitcoins become vulnerable and so does the data that has been locked into the blockchain.
Bitcoin reaching it hard cap of 21million will not collapse at all. Just imagine when bitcoin hit it's all time high of 20000$ ,it becames scarce (limited in supply and higher demand )and it also increased it values , awareness, more acceptability,
more recognition ,more applications into business, etc. world wide .Again Minner may not stop simply because Bitcoin has reached it's hard cap 21 million because, at that time,there must be control put in place to monitor every transaction that come into the block from everyone using bitcoin for various reasons and purpose. In a nutshell, miner will always there to over see that every transaction that come into the block are genuine .