All bitcoins will be found by 2033 I believe and if there isn't enough transaction fees by then to pay the electicity people will just switch off their computers.
Then the difficulty goes lower and the people who keep mining get the fees.
It is a pyramid scheme in the sense that the supply of coins is being limited and so they become rarer over time.
Like I said if they were unlimited, people would never have cared about bitcoin. There would be 0 incentive to use it.