Yes, we can't say '100%' Satoshi mined them, but if you do your own research and understand what Satoshi has done, then one can say '99.9999999999%'.
More like 0.1%.
What will happen if someone moves the coins of the mentioned reused addresses that do contain thousands of bitcoin? A lot! I would not try it.
Theft is theft, you can sugar coat it however you like but it is stealing someone else's money. Not to mention that from a cryptography point of view if a single P2PK output could be stolen, all bitcoins outputs are in danger regardless of their type because there is a short step from there to speeding up the process that lets anyone steal the coins in a transaction while it waits to be confirmed. That makes bitcoin obsolete overnight.