What if one day Satoshi comes back with another invention that he adds on to Bitcoin? That would be pretty cool. Maybe he is waiting for something rather than having "left forever".
Satoshi Nakamoto designed Bitcoin in a decentralized way so in 2025 or future, it helps comes back with development, it will not be deployed directly by him but it will be a proposal, BIP and will need to be supported by Bitcoin nodes before it is available for deployment on Bitcoin block chain.
Not sure about Namecoin and that developer but in the last year, around COPA trial, thermos had a post to share his thinking on probability of different Satoshi Nakamoto candidates.