Won't bitcoin mining become unprofitable at some point

Im not some kind of bitcoin expert, as a matter of fact quite the opposite but wouldn't bitcoin become no longer profitable to mine at some point. Assuming that the price continuously follows the law of diminishing returns where each cycle the average rate of return becomes less and if the rewards will consistently cut in half each 4 year cycle, logic would then dictate that the exponential diminishing of rewards will at some point no longer be offset by the cyclical increase in price. The only solution I guess would be to change the protocol at some point which probably sounds like blasphemy to bitcoiners and will probably never happen. So am I missing something here or will bitcoin at some point become unsustainable? Please feel free to school me.