Cash will be never extinct while people use. I think after 100 years it would be possible but now not. Bitcoin is still weak it needs to grow to 50k at least.
So people will know that its strong and that its not a weak scam coin.
100 years may not really still be possible. Definitely, it could be possible in some places with no demand for cash and with access to technology but would definitely be slower in some places with lower infrastructure since you will have to pretty much be online to transact without cash.
So, all this put into place would make it not go into extinction anytime soon and even longer than 100 years in some countries.
Predicting a definite year is indeed tough. But 100 years are enough for cash to go extinct. Globally countries are shifting towards digital payment medium be it cryptocurrencies or not. But as you said it will require a complete digital connectivity. This might take time. But I believe 100 years from now, it is achievable in third world countries as well.