Hopefully a good amount of them will migrate into alt-coins and create the scenario @haejin is predicting which I've been expecting for some time to happen with BTC going mainstream. My timing was off. I thought BCH would be a beginning. But it seems BTC could have another year of reign.
Going to be hard for BTC to lose its title. It is not longer technological but rather marketing. Bitcoin is not the better mousetrap, just the best funded. Wall Street will keep pouring a lot of money into it.
That said, alt-coins will find a lot of it too. LTC is on a run as is ETH. BTS is starting to gain a bit of traction. We will see others shoot up the board as more utility is offered.
With over 5 million USD per month Dash is the best funded. If you think about ICO money, then the title would go to EOS which should be collecting at $300 million USD a month or something. BTC is a technological relic. STEEM could handle the volume of BTC 100 times and still not feel a thing or face scaling issues. Longer the time frame higher the impact of fundamentals.