Here's how I think it's going to go down:
They will keep the same 7 gentile times invisible presence teaching only changing the year from 1914 to 1934. They'll dump the erroneous 607 date and accept the 587 date for the destruction of Jerusalem. They'll move forward by 20 years, all their other date teachings that are anchored in some way to 1914. The appointment of the FDS will move from 1919 to 1939 - the year that WWII started. They might even say that Watchtower teaching their members not to fight in WWII and their early exposing of Nazi oppression of the Jews, were two of the primary reasons their leadership was chosen and appointed as FDS.
This will be a plus for them in many ways. First it will mean that they get a cleaner FDS that was teaching less error at the later time of appointment in 1939. For example, I think they rejected pyramidology by then. Secondly there's a neat chronological window of time between Jesus' appointment with Satan being cast down to the Earth, and the subsequent woe to the Earth manifested in part by the outbreak of WWII which started just 5 years later (a very short time in the spirit realm where a thousand years is like one day) and which was much bigger in scope than WWI. The current 1914 teaching has Satan anachronistically stirring up WWI in August before he's even cast out of heaven by Jesus on or after October. And of course, finally there's the extra 20 years of time that it buys them.
They'll go this route first to stretch the overlapping generation out further when it's nearing it's end. Then about 20 years later when the 1934 overlapping generation is becoming untenable, they'll drop the 7 gentile times 2520 count altogether and adopt a more mainstream eschatology, saying that presence and coming are synonymous after all and no one knows when christ's presence will be and that Jesus' words about "this generation" had only one fulfillment - the 70 CE destruction of Jerusalem.