Even if it is the same script, you are still looking at adding another hundred or so years onto the empire's lifespan. That's more than enough time to come up with something else and extend the life more. I personally think that Bitcoin is just a system that the governments will look to exploit in the future, and it's not something design to directly increase the life of any empire. Such is with most things, really. It's not built for an authoritative figure to exploit but most of the time they will find a way to do so.
Absolutely agreed, we have to assume Bitcoin was not originally designed to help the empire. It's only an unsubstantiated theory that Bitcoin was created by the Western elites in secret.
My way of looking at the 'finding a way to exploit' issue is that the modern global empire doesn't have enough hard power to control the world (especially since the populations at the center of the empire tend to like their freedoms.) Its modus operandi is therefore to make alliances with the ideas, institutions, inventions, etc. that support freedom. Thus, the hard and soft power together, is enough to control the world.
It's like this with Bitcoin, and with institutions of freedom and democracy.