So you are talking of 119 years later which is more than a century and we can't say what will happen at that time.The future generations will be using Bitcoin as digital currency when it will be Mainstream so why are you concerned about mining at that time.So what do you think they will not have any othe major source of income other than Bitcoin mining?The supply is limited to 21 million and it cannot be increased but Sathoshi have built technology for use by the current as well as future generations.The mining will continue till 2140 which is still very far.The future generations will use Bitcoin and earn through its usage not mining so don't worry about that period.