I don`t believe they will ever do that because its not something they could walk away from or explain its failure to materialize ,however they will always be on the brink of delivering such a message........ in the near future.
Dangling the carrot before the donkey scenario.
Good comment, smiddy. I had always seen this similarly. The 'Good News of the Kingdom' (or whatever you want to call their message, now) is really the penultimate message. Contrast with the final, ultimate, message (see OP).
And really, once they went to the final one, it's that or nothing. I don't see, outside of some 'Jonah clause', how they could renege and stay Jah's vengeance day. The 'Jonah clause' has never been part of the JW narrative regarding the end of the system. Total Armageddon destruction has always been treated as a foregone conclusion. Repentance was never an out.