If there was somehow, a far better piece of decentralised distributed ledger that is invented in the future, this can just be forked into the Bitcoin network and the existing data is retained, or the Bitcoin data is transfered to the new distributed ledger.
exactly this was suggested when "Directed Acyclic Graph" chains were newly proposed.
Proposed by who? A Core developer?
A big problem was how to mine using a chain that's really structured like a tree, how do you arrive at consensus on newly distributed money? And of course, the answer was to start with a satoshi style PoW uni-chain, mine all the coins, then fork to a DAG chain once there are no new coins left.
That proposal is a little naive, isn't it? We've already seen what kind of drama the community had with the scaling debate. That proposal would be like nuclear war if taken seriously.