And that's why I advice to send them the message. If they don't react after a certain time span, it's probably because they can't. You don't have many choices. You either decide to never touch the wallet acknowledging it doesn't fit your moral temperament or you decide to spend the money at some point in the future.
Or, they have not realized the paper wallet is missing yet or they are still hoping it was lost somewhere inside their house. Or, they just bought Bitcoin and decided to not touch them at all for a span of 1 or 2 decades. Or, who the heck knows.
I can only agree it is morally incorrect to play the 'finders keepers' game in this situation. Remember there are insanely large wallets that have not moved for a decade and started moving only this year (or last year). This could be yet another theoretically lost one, but practically who knows. It could be years from now that the owner will finally come to the surprising reality that their paper wallet has vanished.
I also support the idea of publishing the public key here just in case the owner has no other backup besides the one they lost on the beach. And if ownership can be proved, they can have it. If I was OP, I would either hand it out to the right guy or, if that is not possible, then I would just consider the 0.6 BTC as yet another Bitcoin lost forever.
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Regards,
PrivacyG