Evolution happens due to mutations and natural selection, eternal living will still bring new kinds, bacteria still exists.
Natural selection occurs through differential rates of survival among variants. If every variant survives and reproduces, there is no differential survival and no selection effect. This is so obvious.
Further reproduction is exponential. If every progeny survives and if older generations so not die, population of organisms increase without limit. Earth has limited resources. So how is it possible for every individual to acquire enough food to survive.
Finally do you understand what death is. It's an entirely chemical and biological thing. The organism is a chemical factory and death is an irreversible breakdown of the process systems inside the factory either due to lack of raw materials to sustain it (food) or due to corrosion of vital components (old age or disease).
Finally under ideal conditions, certain bacterial cells and even some plants and fungi can indeed live forever. They rarely do due to resource stress or predation. More complicated organisms like us has too many internal parts to indefinitely work as factories without something or the other breaking down. This is old age. Death is not inevitable for all life, just very very probable. And the fact that it occurs is what drives evolution as it selects those who die less often and reproduce more due to better traits over those who do not.
