Suppose we finally reach a point where we don't treat races differently in any sense that matters. There's no more even unconscious discrimination. The structural barriers that favor whites more than other races and some non-whites over other non-whites, even when no one intends to do harm, are gone. There are no more people who have negative attitudes toward people because of race. Yet people continue to use racial terms the same way we continue to use ethnic terms (e.g. Italian) even when there's no prejudice or societal structures making things difficult for those ethnic groups.
If you don't think races exist now, you'll obviously not think they exist in such a circumstance. But if you think races exist now, will they still exist under such circumstances?