America isn't 500 years old. The Indians had separate nations and not one civilization. In South America and Mexico, though, there were civilizations which developed and ended and so on just as any other peoples do.
There would be no America as we know it.They would probably be living just as they did in the past.Remember the European settlers introduced guns and money so they would still be using bows and spears and living as they used too.
Any answer given would technically correct because you are asking a hypothetical question. We will never know. Look at Tecumseh....he dayumed nearly unified the Shawnee Nation and several major tribes and whupped the whites....mighta have too if not for his idiot brother and the British had given the support they promised.