But are we sure the maths behind Satoshi's "formula" is robust for the next 100+ years?
The truth is we are not. The ones who say they are sure are either lying or don't really understand it.
Although we are not sure, there is a high degree of confidence that it will work in the future.
To paraphrase Half Finney:
Every day that goes by and Bitcoin hasn't collapsed due to legal or technical problems, that brings new information to the market. It increases the chance of Bitcoin's eventual success [...]
This can also be seen as a manifestation of the Lindy Effect.