I wouldn’t put it past him to try to run as an independent. Even though many states have sore loser laws to prevent failed major party candidates from launching an independent bid, I imagine he could find a way to weasel around that. The other possibility that I see him pursuing is getting attached as a VP candidate to a Trump ticket. RFK Jr has already stated that he would be willing to accept a position in a Republican administration, and has been flattered by compliments from Trump.
His belief is using a free market approach on the environment.
Even if that were to be true, the only thing shown is that RFK Jr has no chance in the primary. Though, I am not convinced that is true when in 2012, an incarcerated inmate won 40% of the primary vote in WV against Obama. https://abcnews.go.com/blogs/politics/2012/05/prison-inmate-wins-more-than-40-of-democratic-vote-over-president-obama-in-wv-primary
It is interesting that you bring this up, because RFK Jr. likes to tout that he has a high favoribility rating. However, when that rating is broken down, that is being entirely driven by Republicans. His favoribility is dismal among Democrats.
This is how RFK Jr tends to operate. By taking a statement with a grain of truth, he extrapolates a masterful inveigling.