"No one actually knows what will happen when the cap is hit and no more Bitcoin will be rewarded for mining. The idea is that the network will be self-sustaining by this point. Transaction fees are expected to compensate node operators since mining will no longer yield coins.

It is possible miners may flee the Bitcoin network for more lucrative currencies. This would harm the network and make the dreaded 51% attack more possible. It is also possible the Bitcoin protocol will be changed to allow for more than 21 million coins.

This IS possible. Code can be changed. One wonders what might happen to BTC value was this to happen suddenly and without warning. Insiders would make a killing shorting the coin if they knew ahead of time. However, this type of speculation is for another essay."