Which of the these Traitor Primarchs is the closest to ‘defecting’ back to the Imperium?

I’m excluding Omegon, who for all we know is already a loyalist.

Angron and Fulrgim are too far gone, with no chance of redemption.

Lorgar is a zealous-fanatic and the only way I really see any chance of him turning back is if the emperor’s physical body dies out ascends to warp god-hood, after which the emperor’s light overshadows the ruinous powers.

So realistically, out of Magnus, Morty, Perty - who is most likely to become a loyalist again?

Headcanon says probably Magnus, if he’s ever able to absorb even a small fragment of his noble shard.

Edit: I know realistically none of them can, but I after playing Space Marine 2, I got to thinking that no way Magnus is too happy knowing that he’s been manipulated all along. What if the other primarchs has similar thoughts?