Generally, a party has successors that would benefit from the contract.
But without seeing the contract, we don't really know. Perhaps it only bound the original publisher, and not the author, but some other contract had bound the author to only publish through that publisher, and that publication contract is no longer in force. Who knows, the article doesn't tell us.
And dead people don't have rights past what they have decided on inheritance and even this can be sometimes overturned by justice. This is the reason wealthy people sometimes give their wealth to a foundation but if the foundation doesn't find a way to make it sustainable and money runs out it also ends up dissolved regardless of the cause it was bound to serve.