Interesting... So you think the Beatles may well still happen even without the King?
Yes, and another factor is that in the fifties, the most popular songs were covered by multiple artists. A given song might appear several times in the Billboard Magazine Top 40 (or Top 100, etc.). Radio stations had to choose whose version they would play.
Elvis did not write his songs. His absence leaves "holes" in the charts that can be filled by others. "Heartbreak Hotel" and "Hound Dog" would not have sounded the same, but they still could have been hits. Before Elvis, Bill Haley, who was white, had a big hit with "Rock Around the Clock" in 1954, establishing the term "rock and roll" and the doo-wopp beat pattern. The next year, Chuck Berry, who was black, began to compose, play and sing material that would earn him recognition as perhaps the single most influential individual in the course of the first decade of rock and roll music.
It took an incredibly short amount of time for Haley, Berry, Elvis and Buddy Holly to leave very important footprints on music. Haley fades away, Berry goes to jail, Elvis gets drafted and Holly is killed.
As American rock went into a lull, the Beatles were still aspiring musicians looking for material. True, John Lennon did say "Before Elvis, there was nothing." But Elvis did not compose. One less role model would not have stopped them. Their style would have been a little different, but they would still have been the British complement of evolving soul music. Of course, they were not alone. You still had the Kinks, Rolling Stones, Herman's Hermits, etc. waiting to invade popular music worldwide.