There are already technically better cryptos out there than Bitcoin and I will be astounded if Bitcoin does not lose its market dominance in the next 20 years, let alone 100!

But hypothetically there is always the possibility that if the miners are crumbling due to block halving, there may be a new Hard Fork proposed to remove the block halving and stabilise the mining reward.  It sounds like sacrilege now to remove the 21 million limit but it can happen and if the alternative is a collapsing network with fewer nodes and security compromise it may be a lesser evil.

We have a lot of time to figure it out.  Lets just make sure we survive the 2017 Hard Forks first! :)