Well sort of. Some believe that very early in our evolutionary history there was competition between different DNA encoding schemes and different ribosome conversion complexes.

but at some point one was good enough, and then evolution was occurring WITHIN a single system, and that evolution was happening so fast it crushed all alternate DNA models, etc.

No one believes our current DNA-robosome model is somehow optimal... its just that evolution has sunk too much advancment energy into this line. No other line can complete.

In a similar way, I think evolution may begin happening at a higher level (e. g. how societies are organized or such). and the implications might be so profound that the small losses of efficiency in our current biology is just inconsequential for evolution.

bottom line:

evolution can continue even if the human form does not change -- though I think it could actually be completely replace by a non-human form.