I think likely Satoshi Nakamoto is dead and his coins are lost forever. Because they were never moved.
You forgot to eliminate other possibilities:
1. The private keys are lost to the early coins. SN is still alive and well, he is just clumsy.
2. The keys are locked up (Tulip Trust) in some kind of legal problem.
3. The entity who is SN keeps them for some kind of further plan.
4. If the project was a government owned one, the coins are government property.
5. The owner of the coins doesn't know he/she has them. (inheritence)
etc.etc.
Then the market cap of bitcoin is a lot smaller