So much BS:
There have indeed already been several sects splinter off of JWs:
Jehovah's Witnesses splinter groups
Keep in mind that they weren't known as JWs until 1931 so any sects that developed as offshoots before (see Blondie's post above) are technically NOT splinter groups of JWs.
From one point of view, Rutherford can be considered an apostate of Russell's teachings and that he started his "own" religion when he basically conducted what in modern parlance would be called a hostile takeover of the WTBTS.
Pre-JW schisms :
A number of schisms developed within the congregations of Bible Students associated with the Watch Tower Bible and Tract Society of Pennsylvania between 1909 and 1932. The most significant split began in 1917 following the election of Joseph Franklin Rutherford as president of the Watch Tower Society two months after Russell's death. The schism began with Rutherford's controversial replacement of four of the Society's board of directors and publication of the The Finished Mystery.
Thousands of members left throughout the 1920s prompted in part by Rutherford's failed predictions for the year 1925, increasing disillusionment with his on-going doctrinal and organizational changes, and his campaign for centralized control of the movement. William Schnell, author and former Jehovah's Witness, claims that three-quarters of the original Bible Students who had been associating with the Watch Tower Society in 1921 had left by 1931. In 1930 Rutherford stated that "the total number of those who have withdrawn from the Society ... is comparatively large."
Between 1918 and 1929, several factions formed their own independent fellowships, including the Standfast Movement, the Pastoral Bible Institute, the Laymen's Home Missionary Movement founded by P. S. L. Johnson, and the Dawn Bible Students Association. These groups range from conservative, claiming to be Russell's true followers, to more liberal, claiming that Russell's role is not as important as once believed. Rutherford's faction of the movement retained control of the Watch Tower Society and adopted the name Jehovah's witnesses in July 1931. The cumulative worldwide membership of the various Bible Students groups independent of the Watch Tower Society is estimated at less than 75,000.