Dotcom companies went down because there were too many of them offering things there wasn't a big market for. ICOs may not go this way because the main thing they deal with - their foundation is simply human greed, and you can count on that to go on and on. Just look around and ask yourself why are there still casinos and gambling halls when we all know they're just a legal way for robbing people.
greed isn't infinite. at some point you gotta offer a glimmer of delivering on your hype. casinos offer it every time you go. that's why you come back.
icos can't continue for a decade without more than a few people actually wondering what this money is actually doing. as soon as that happens en masse it's over.