I am unable to find much work regarding what happens after mining ends. A hundred years from now does seem like a long time, but to ignore it is irresponsible. Assuming the community consensus is to shun regulation, here is what I imagine will happen. Everyone will flock to the largest transaction processor since they will likely offer the lowest rates. As their market share grows they will bankrupt all the other processors by offering even lower rates. When the smoke clears they will look around for any other competition like VISA, if they still exist. If VISA has a rate of 2%, they will offer 1.9%. They will be so large that the cost of entry for competition will be prohibitive. This would seem to defeat the entire purpose of the Bitcoin spirit.

The solution: In processing transactions there must be an incentive to maintain an optimally sized network for competition and security of the blockchain. It must be built-in.