My question is if he does return, how?
His ability.
We know practically nothing of it.
Just some assumptions.
Little is known of Fyodor's ability; thus far, it was able to kill someone with a single touch. Moreover, it is not restricted to skin-to-skin contact. For instance, when he was grabbed by a government agent wearing gloves, the agent was nevertheless killed by Fyodor's ability.
Another hint towards the nature of his ability is that it did not turn against him even when affected by Tatsuhiko Shibusawa's mist, which separated majority of affected ability users from their own powers. It even declared itself to be the "punishment" to Fyodor's "crime" and stated that they were closely linked.