Naaaa. Manchin is a non-event. There is zero chance Nikki would ever run as an independent.
Just like stocks, I'm gonna make a bold prediction. She's gonna be the GOP candidate.
Edit:
And I think she'll take the Presidency by a landslide if Biden is her opponent.
Keep in mind that Manchin or some other NoLabels candidate would only need to take more than, say three percent, to make it a YUGE event. Don't think in terms of whether someone can win or not. Even three percent would be total Rumsfeldian chaos.