Chaps, thanks.
You all make some very valid points and you have some justifiable concerns. If not handled correctly a sequel could indeed be a disaster...
...but I wouldn't let that happen.
I trust you'll forgive me for not answering point by point (on my phone as the render hamster squeaks away) and quotes etc are a nightmare to do right.
IF, and it is an if, it were to be a sequel it would be the same protag. I say that for although the story doesn't end on a cliffhanger, it does end in a cracking way. I'll be honest and share, the ending popped into my head one day. I suddenly had an image of the very last scene - and that's what made me write the game. Now, this doesn't mean your story is fixed, but the arc is. Your choices do indeed matter. Who you romance, whether the mission is a success, what happens to and on Ophion, indeed whether even everyone even survives (and some you may decide you don't want to...) is all down to you. But your MC is not the only player in this game...
IF it were to be a sequel there would be no hard reset. I have a way to make the choices roll over story wise in a logical way that is actually manageable from a dev point but I'm finding your concerns to be really interesting. This is a superb sense check of will it work, is this what they'd want, which by myself I would be merely guessing or perhaps even missing a trick.