Although Beethoven was not completely deaf until toward the end of his creative life, he began to lose his hearing much earlier. This could well have had an impact on his attitude toward life and as a result, the emotional focus of his music. Also, although he could still compose music after losing his hearing, he could no longer play concertos and the like, which required him to be able to hear what the rest of the orchestra was doing. That was a major source of income for all composers in this period. This might further darken his attitude.
Since some of Beethoven's best and most powerful music is also his most anguished or angry, maybe he might actually have NOT been as great a composer if he never lost his hearing. How about that?
But none of this would change the world.