Although of course it seems unlikely, all good things must come to an end and someday, in the distant future, the blockchain technology will fail. When it happens, what could replace it? Is there anything out there that functions similarly and just as good and reliable as blockchain? More importantly, if nothing replaces it, what will happen to cryptocurrencies then? Any ideas?
Blockchain isn't going anywhere. It's a fundamental technology and will continue to be developed and refined.
Whether individual coins will continue or fail and be replaced is another question.