Except bringing Mima back would mean Zun will have to explain things the most compare to other char.
Then avoid bringing her back. Although, what Theorist pointed out makes alot of sense concearning returning characters. Alice just popped up out of nowhere, ditto with Yuka. Did anyone question anything of where they've been or what they've done all that time?
No. Not at all.
However, in Alice's case, her reappearance just raised alot of stink about why Makai or Shinki wasn't mentioned in her dialouge or profile, but given what happened in MS one can already make a valid assumption as to what she's been up to, so it doesn't really matter that much.
ZUN should suddenly take out Marisa and Reimu as playable character for Touhou 13, 14 and 15 (if that ever occurs) just to piss people off. I wonder what would happen.
Depends on what character(s) replaces them.
God help you if it's Mima.
You know, that's actually not a bad idea, hell, I'd be happy to see Cirno as the next MC for a change as opposed to the same ol' miko and the same ol' witch.