Then what is the problem with a sequel concept? There is lot of potential between the twins, the character writing is very good, so....
No problem with a sequel. What I was trying to say is that the story of
this game seems to be past the middle. A sequel is a new game.
I believe that it would be better for everyone if the story part-1 ended at say 0.85 or something and then with the experience and all the developers have made they started a sequel after a few
months so they could figure an equally enamoring story that is well thought etc. improve some of the technical aspects, recharge their batteries etc etc.
The only stick-up I can think is that if part-1 finishes there will probably be many quite different endings. Picking one as the "canonical" ending may ruffle some feathers.
On the other hand, a "game completed" tag on this one would IMO attract people to this game and the quality of this game would lead them to go for the next one. I.e. I think it is the best scenario for all involved: The developers, the patrons, the loyal fans and the newcomers.
And of course, the side-benefit of discussing the sequel with people that go "That's utter garbage compared to the first game!" or "This one is golden while the first one was utter garbage!" and similar hyperbole and exaggerations.