it is not possible to answer at all because you are asking me to predict what is going to happen in a century from now. it is already hard to know what the future in 5 years is going to be like let alone 100. with that said the design of bitcoin is based on the assumption that when block reward becomes so small the total transaction fees that a miner receives should cover their cost of mining in the future.
Projections and analysing the future look unreliable or unreal. We can see how many companies and government made some plan this year but no one knows if there will be a disruption of such plan by coronavirus pandemic.
That's why Lord Maynard Keynes said" in the longrun we are all dead" so our analysis should be in the short run because we are still alive.
That's very valid