They won't end for a long time. Even once crypto is a fully established part of everyday life, it will still be evolving, and new opportunities and gaps in the market will continue to arise. Really it's limited only by human imagination and innovation. I'm sure we will continue to see ICOs for many years to come.
I think the history of websites offers good indications of the possibilities. There are websites now that wouldn't have even been dreamt of when the web started to become popular a couple of decades ago, and new sites are arising all the time to fulfil new needs and take new opportunities.