Bitcoin will not collapse. Even without miners getting any more rewards for mining a bitcoin, the reward they will get from the transactions fees of processing bitcoin into the blockchain will be enough for them to continue. Bitcoin will be more scarce by that time, and I’m sure the price of it will be far higher than what it is today, so definitely the miners rewards from transaction fees will be sufficient for them to continue mining. The protocol has been designed to be a continuous process, so I don’t see bitcoin mining coming to  an halt if there are not more bitcoins to mine again.