This is an edge case. The vast majority of intellectual output loses value extremely fast. If a new Kafka comes along and their writing becomes popular 30 years after publication, they will have 0 issues getting a fat contract for a new book.

Justifications for copyright are always built on edge cases, seemingly moral justifications of an empirically immoral practice. Yes, it'd be nice if a single handicapped mother of 2 coild see her children rise out of poverty thanks to her writing talent after 50 years. In practice, this person doesn't exist and building society around that scenario is not a good thing.

These 'what ifs' have the same value and do the same damage as 'who will think of the children' do for human rights.