Bitcoin will be the future reserve currency for a few decades to a few centuries at least.

If we lose internet availability for most people and microprocessor mass manufacturing due to energy bottleneck (not unlikely), it will be superceded by a non internet-protocol based reserve currency in the next civilization phase. Maybe back to gold, maybe something else; influenced by bitcoin but lower energy use and lower tech. Like monks doing mass human pen and paper hashing (something easier, not sha256) in a mirror-semaphore network of monasteries, to keep big money transactions honest, or at least as honest as possible.

Notion of protocol is powerful concept, even without computers or internet.