Lots of very basic questions!

A quick shortcut might lead one to suspect that a virus is moving towards less virulence because if it kills its host it will no longer be transmitted. But viruses, which are responsible for diseases like AIDS or the flu, show the opposite. For SARS-CoV-2, this argument of a possible decrease in virulence does not apply, as it is transmitted before the most harmful effects for the host. On the contrary, the Delta virus appears to be more virulent than its predecessors.

Another characteristic feature is transmission, which by increasing it pushes back the level that should be reached for collective immunity. As a result, some specialists say that this threshold cannot be reached without drawing any conclusions about the lack of interest in a vaccination that will prove its effectiveness every day in the most serious forms.

All of this to answer the beginning of your question: yes, among the possible developments of the virus, some can be selected that would cause this virus to escape the antibodies. And vaccinations are one way of increasing this selection pressure. For the time being, the reservoir of infected people is still large enough, it is rather better transmissions that are preserved in the virus evolution. This would explain, for example, why the beta and gamma variants remain in the minority in France ahead of Delta.