Greetings,
Obviously, due to it's holdings alone, the Watchtower organization can continue as long as it cares to. However, it will continue to be less and less relevant as time goes by, owing to the fact that it has not made a succesful transition from an apocolyptic sectarian group, to a "denomination." The Seventh Day Adventists, and others have made the transition by building hospitals, schools, colleges, etc. nailing down their tent pins so to speak, while the Society has continued to eschew the "world" and it's ambitions for the most part.
Regards,
"The one true Church, dear friends, is the church of the Bible. There never has been but that one true Church. All others are false, and if I build up another church I would be building up another false one. That is not our proposition at all."--C.T. Russell