If the macguffin completely destroys the central conflict of act 1 (and maybe even more!), I'm sorry, but I'm not going to straight up believe Larian's writing is that shit. There will be a cost. Maybe a reward for faithfully serving someone in particular. But a handout? For every fully symbiosed character? Nah. There's no way in hell I'll believe you that you'll end up "just fine" down that path. You'd have to be the Dark Urge and about to ascend, fuck a puny tadpole and its shadowmagic.
You're dwelling way too much on act 1. Choices will have consequences...like locking you our of alliances and costing you party members. But it is very very unlikely to lock you into a bad ending...it might lock you down an evil path but even that is unlikely as Act 1 is less than a quarter of the game so around a fifth or so. But in case you haven't been paying attention, Larian isn't going all in on punishing bad endings where you better be nice or you die or go sit in a corner with the dunce cap on. This game has a full spectrum of endings including where you can get a satisfying evil ending. Not to mention that evil gods like the dead three and Shar aren't just the best of buds just hanging out for fun...no, each of them wants to come out on top at the end of it all...preferably with the power of the other three. If nothing else you'll almost certainly be able to play them against each other, potentially even getting one of them to remove the tadpole.
