http://www.forbes.com/sites/kashmirhill/2014/03/06/bitcoin-creator-returns-to-internet-to-say-i-am-not-dorian-nakamoto/
Legally speaking, if a person is missing for long, and there is no physical trace of that person, whether alive or physical remains; then under the Forensic Law, that person can be declared dead only seven years from the last contact with that person.
Here, we have an online comment from 'Satoshi' in March 2014. So, if there is total silence from him since then, seven full years must necessarily elapse, before he can be considered legally deceased.
That means a legal certification of Satoshi's demise can be made only after March 2021. Hopefully, this rather ungainly prospect should impel 'Satoshi Nakamoto' to make periodic online comments; so as to at least push that date even further, if not to entirely scotch such outrageous rumours!