Jeova witnesses or mormons are internationaly everywhere, still existing after 3 centuries. That's why against your hopes, i think scientology will survive somehow, maybe as rons org maybe as both, who knows: they gained so much power (just like the vatican did 1 century after jesus died), so much money, so many buildings (just like the vatican), so i really dont see them going away in the near time, unless tom cruise, john travola and mike rinder do a je accuse on the media, together...
Mormons have helped to build hospitals, built their own world-class university, denounced the misdeeds in their past, and have a truly ethical way of life -- assuming you enjoy wearing secret underwear. The Mormons encourage marriage and family in their own clergy as opposed to SO splitting couples apart and encouraging, or even forcing abortions. The Mormons offer positive family values for a 10% pre-tax tithe and brother, you had better lengthen your stride if you want to make it.
The JW's are a miserable little cult full of child-molesting elders. The JW's were over after Jesus missed the 1914 appointment that the Russellites had set for his return. Like CoS, the JW's are stuck with their absurd past and wicked leaders in PT. The JW's are saddled with a screwball eschatology in the same way that Scientologists are stuck with a screwball cosmology.
I see the JW's in the same camp as Scientologists: Miserable, American-made Cults that were exported to target audiences. The JW's are definitely low-budget Cultic Misery built around stats. The Scientologists are middle class to affluent built around stats. Whereas the JW's will show up at your front door trying to sell you cheap little books printed in Brooklyn, the Scientologists will mail you their glossy hallucinations that come courtesy of Henning Benndorf's unique graphic madness.
The JW's and the Scientology offer the same Cult mentality with different messiahs. The JW's do not believe in the Trinity and so offer you Jesus and introduce him as the brother of the Archangel Michael. Scientology offers you a drug-addled Satanist whose ego knew no boundaries and whose followers think that wog law is meaningless. Scientologists and JW's have both condemned themselves and their groups to an eternally fringe existence by their own actions.
If the JW's and Scientology merged, it would be one hell of a funny new religion. Imagine it: The JW's doctrinal prohibition against blood transfusions could be explained by claiming that BT's could be unstuck from one body and flow to another via blood transfusions. There are so many possibilities here!
To Lulu_belle's point: All of the JWs' from 1914 are dead and so JW's nowadays do not remember the prophecies that had Jesus returning in 1844, then 1914, and so on. All the modern JW's know is that Prince and Michael Jackson are somewhat secretly JW's!