If you think about it you will realize that... Hal can't be Satoshi, because Satoshi is a
disambiguation.
Quoting a known phrase from V for Vendetta:
Beneath this mask there is an idea... and ideas are bulletproof.
So, Hal being an idea? Nah. If we're talking about the programmer who developed Bitcoin and disappeared in April 2011, he might be; but that “might” will remain unknown. That guy who gave us that divine gift is gone for good, his software is the only thing left to be remembered.
So if someone "finds out" 50 years from now who owned those private keys, chances are this is just a random coincidence and collision that proves nothing.
True. As time goes by, these private keys have more chances of being found by someone else. When Bitcoin will have changed to quantum safe algorithms, someone may pretend of being Satoshi by searching the, insecure by that time, 1 — 2^160 range. In other words, in the far future, there won't be any ways to prove you're Satoshi.