Nope unless we are going to have an apocalypse which can end the entire earth in next 100 years, bitcoin is definitely not going to be the last currency. I am saying this because we all know quantum computing is already a threat to bitcoin not in next 10-20 years but definitely in next 100 years and once it's a threat bitcoin will not be that secure and that useful and ultimately we'll have some other currency in its place.
You do realise quantum computing is just as big a threat to fiat, right? If it reaches that level, it can crack any current bank's encryption just as easily. And if I were some sort of financial terrorist with access to a quantum computer, it would be clear to me which target would cause more disruption.
That said, security can be upgraded. We know what the threat is, we can see it coming and we likely have ample time to make preparations. It's not like everyone is just going to sit there and watch while it happens.