Yeah, the part about the Vishanti had me wondering, too. Makes it seem like they weren't involved in transferring the title back to Strange, or did so only reluctantly (though, again, why not just chose someone else?). It does also make it sound like Strange hasn't realized the full extent of what he's done, since the Vishanti removed him for being mortal and for failing, not for using questionable methods, and the solicit makes it seem like it's only a question of whether he deserves the title because he's close to failing again.
Trying to figure it out, I was wondering if the arc wasn't entirely over yet, or if there was going to be a part 2. Partly because it seemed implied that the Vishanti gave Loki the title in order to do something (and Cates said that we should be asking 'why' he was Sorcerer Supreme while reading) and that's been left undone. Even rebalancing magic is something any Sorcerer Supreme could ostensibly do with the spell if it wasn't tied to Zelma. So we haven't seen that yet. Though this is probably me reaching because I thought Loki being Sorcerer Supreme was a neat concept and I'm sad it's over so quickly.
The other part of the story that's been left undone, as I kind of mentioned in the first paragraph, is Strange realizing that he crossed some major lines. Iirc, the first solicit for Damnation does mention something about showing the world he can still be a hero, so maybe there has been some fallout. Still, that's really why he should be questioning his fitness as Sorcerer Supreme now, not because the situation looks bad (okay, the ability to do the job is also important, but I'm expecting it to be more of a comic book 'Oh no! Will our hero fail?' sort of thing than him actually tanking and burning). Granted, his realization that he was wrong could all be handled with internal character development with no (or minimal) need for Loki to re-appear in the story and thus wouldn't require the arc to continue. Realizing that Loki actually wasn't threatening the world (or Zelma) like Strange thought might be an impetus for him to re-evaluate his actions (assuming it isn't some authorial trick where he's been evil this whole time, which would really undermine the entire story arc, as I've probably said). The easiest way to achieve this would be for Loki to show back up again; however, I don't think it's strictly necessary for Strange to realize that Loki may have been in the right, so much as it is for him to realize that he himself was in the wrong.