When the old guard die out, or decrease to a managable percentage - (those who remember "the generation of 1914 will by no means pass away") the society will gradually phase out 1914 as the concrete start date of the last days. They'll become more wooly. Phrases such as "evidence clearly shows we are deep in the time of the end", and "who can reasonably doubt", "world conditions confirm" will become more frequent.
To keep the "we're the one true organisation" doctrine, they'll continue to harp on the theme that "Jehovahs evident blessing" shows they were chosen at some point.
It will be a long set up to the WT that will state "While some have pointed to specific years as the start of the last days, we bring in a heart of wisdom by reflecting that the exact day and hour are unknown, however we are assured by events we see every day that fulfil reliable Bible Prophecy we are nearing the climax of the end of this system of things and that Jehovah's Kingdom will soon usher in a time of deep joy for the faithful who will survive the upcoming day of Jehovah..."
Half the congregation won't notice, and those that do and who are upset by it will be too old to change, having invested 40,50,60 years of their adult life to the org.