So what happens next in South America and the West coast?
How large was the founding Viking population and how large was the population before the loss of contact with the Old World. What was their doubling size
Assuming that they could somehow get to the New World and become the dominant population, they would also bring Indo-European languages to the Western Hemisphere with them.
I've always found the whole idea of Indo-Europeans bringing their languages to the New World highly improbable. I could see a group of peoples, a Para-Indo-European speaking group being able to maybe migrate across Beringia. East Asian migrations will still occur so the cultural development of the New World would be different from OTL. I think that some populations may have more "European" looking features, but that is just a drop in the bucket. Native Americans would still be culturally distinct and people who look the same who fought each other throughout history. So any contact between Europeans and Native Americans would probably be as it was in OTL. However, linguists in TTL may be able to find some distant linguistic links between some Native American languages and the Indo-European languages.