Yes, the theory of evolution would still be true even if Charles Darwin had never existed. While Darwin's work on evolution, especially his book "On the Origin of Species," was groundbreaking and played a significant role in shaping our understanding of evolution, the concept of evolution itself is based on empirical evidence and scientific observations that extend beyond any single individual.
The theory of evolution is supported by a wide range of scientific disciplines, including paleontology, genetics, comparative anatomy, and molecular biology. These fields provide abundant evidence for the processes of natural selection, genetic variation, and common ancestry, which form the foundation of evolutionary theory.
Even before Darwin, there were scientists and naturalists who had proposed ideas related to evolution and the change of species over time. Notable figures include Jean-Baptiste Lamarck, Alfred Russel Wallace, and others. Therefore, while Darwin's contributions were significant, the theory of evolution would still exist and be supported by evidence even if Darwin had not developed his particular formulation of the theory.