They will loose worldwide their charity status.
Over time, I think the GB will slowly close the branch offices in countries around the world and administer the individual congregations from Warwick because doing so would bring them several advantages:
Of all of the wealthy developed countries in the world the U.S. has the strongest constitutional protections for religion, so while WTBTS may lose it's tax-exempt status in other countries they will likely keep it in the U.S. Also American courts, both state and federal, usually try to do anything they can to toss out any case brought against a religious organization for fear that such a case might be impacted by the free exercise clause or the establishment clause.
If they get to the point that Warwick is the only thing left other than the congregations themselves then the GB gets a bigger percentage of the money coming from the shrinking donation pie.
As for any abuse that has occurred or that continues to occur in nations other than the U.S. the GB will be able to shield themselves from financial exposure.
Finally, as the membership continues to dwindle and Kingdom Halls around the world slowly close the GB will be free to sell the real estate and take the money for themselves (without a local branch office taking a cut) so that they can support the Warwick complex for as long as possible.
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In the end they may devolve into an online-only organization where JW . org has a paywall section where dubs are expected to pay fee of something like $19.95 a month to demonstrate that they are "active" witnesses. Although such a scenario would probably take many decades to develop.