It would certainly be... a choice to lock the best ending behind Dean's route. But I just don't think it'll play out that way.
As someone that spent basically the entirety of their time playing, convinced he would have some kind of heel turn. I'm just not seeing it. Not this close to the end. At some point we need to accept he's just a normal character that needs a rewrite to his route. Because right now his most notable moment is everyone else's day 19 when his romance subplot with Dave finally ends.
I think it's genre paranoia to not trust the character who's "just nice".
But to feed into my old suspicions, he still has moments that make me hesitate. That vision in the forest where he doesn't react right to Dave bloody while also armed with a gun. When Tyson finds Dave dying Dean is somewhere in the forest allegedly looking for Dave. He's intentionally left out when Thanatos goes through the list of who died after Dave does. Tyson is shot immediately, Orlando right after, Hoss, Roswell, Benson and Oswin all burn up in the fire with Sal maybe still being alive right outside. The fact on both path A and B his location is unknown at the "to be continued" point.
Thanatos even mentions that Dean has so far always been good on every timeline. But he also admits the group has never made it this far accompanied with the knowledge some of his memories have been deleted.
I don't see him working for Memphis. But I can see him breaking under the threat of death and abandoning the group. I believe Sal even mentions Dean and Tyson as the most likely to snap first. But with Tyson (who I'm personally worried wth he's up to on path B) he's at least loyal to Dave no matter what because that's all he has. Dean has a nice life outside of the mansion he'd probably want to get back to.