That wouldn't mean there are no other "outside worlds" outside of Gensokyo - there would still be another "outside world" where Rinnosuke gets all his stuff and where Maribel and Renko live in, which means there must be another world so identical to ours - possibly a parallel universe? As for our world, which is now the inside world, that would make entry to Gensokyo much easier than we thought.
What if Maribel and Renko time-traveled through Gensokyo and screwed things up to cause multiple time paradoxes?