While I certainly don't think all things in the digital space map perfectly to things in the analog space, there's literally centuries of precedence for descendants of someone who's deceased to make decisions about publicly releasing their journals, correspondence, unfinished manuscripts, and so on. Most of Emily Dickinson's poems were published after her death by her sister; author John Kennedy Toole's Pulitzer-prize winning novel A Confederacy of Dunces was discovered and submitted for publication by his mother after he committed suicide; Franz Kafka's The Trial was only published because Kafka's executor defied his dying wish to burn his unpublished works.

tl;dr: I don't think the ethical questions here are affected by whether the deceased's writing takes the form of ink on paper or bits on digital storage.