I don't think the Raku ends up alone option is on the table as of yet, unless Marika does end up being the promised girl after all and the guilt over not returing her feelings ends up causing him to reject everyone. But somehow I doubt that's where the story is going.
If my theory about the last volume covers mirroring the first ones, then we are going Marika-> Tsugumi-> Onodera > Chitoge (or Onodera + Chitoge)-> Raku and the final girl. At the moment, things are pretty much saying that Raku and Chitoge are going to end together, even if he's still unsure over his feelings about Onodera.
Well, I'm just happy Komi is going to be (hopefully) doing what he always did best: character drama. That, and hopefully once he's done with this romcom, I hope he does something similar to Double Arts again. Nisekoi had been fun, great at those occasional arcs, but I want a fantasy story by him again.
Nisekoi
Chitoge is best end mathematically.
instead of losing 4 girls and keeping one from picking anyone else, you gain 2 girls and lose 3 because Tsugumi comes with the Chitoge package.
I don't think there's a way for Tsugumi's feelings to remain unanswered at this point.
They'll probably become known to Chitoge and Raku, alongside Claude discovering that she's a girl.
Probably a penultimate arc before the Chitoge/Onodera choice is made.