Why not? The MC in Acting Lessons killed somebody. Pinkcakes isn't writing a Disney Harem story, that isn't his style.
I think people are going to be quite surprised as this story progresses.
For Quinn. Yes.
He doesn't have to buy 50 grams of Coke, he's not Scarface. It's a one time thing.
And your last line can be said for almost everything that has happened so far. MC made pancakes, great, now what? MC got drunk, great, now what? MC fucked X, great, now what?
It's a plot point, it can go where Pinkcakes wants to take it.
But let's use a popular theory I see around here as an example of where this plot can take us. Riona. I see multiple people speculating that she can get into the bag of coke and potentially die(because Pinkcakes is going to go from killing a major LI to a minor side character, lol).
If there is no cocaine, she can't get into it, therefor she can't die.