If it is of significance to the living world, then yes, it'll be published. Anne Frank's dairy is an example of that.
Is it the right thing to do? I'll leave the question for an ethicist.
From Wikipedia’s page on Anne Frank[1]:
> Otto, the only survivor of the Frank family, returned to Amsterdam after the war to find that Anne's diary had been saved by his female secretaries, Miep Gies and Bep Voskuijl. He decided to fulfil his daughter's greatest wish to become a writer. He published her diary in 1947.
Her diary was published because her father had reason to believe it was something she would have approved of. In Márquez’s case we’re talking about going against the author’s expressed wishes. The situations are polar opposites.
Also, 'wanting to be a writer' does not necessarily mean that you would have wanted to have a specifically private piece of writing published.
This, on the other hand, is someone going against explicitly stated wishes. It's not a very comparable situation.
Tell me you've never read Anne Frank's diary, without telling me you've never read Anne Frank's diary.