(also I’m 110% on a watchlist with the shit I google bc of this game lol)
Yes but I cannot really imagine this possibility is part of the plot. IO would show us his death if he was going to die. Also 47 as a professional would make sure the syringe contains air before attempting to kill him with it.
I would answer this with no if not a new amnesia dose fell from the sky into the hands of the Constant at the last level. 
Well they mention that they’re trying to perfect the serum to have the ability to erase specific memories and then they could commercially market it. Given that I’d wager there’s more than 2 science cars on the train (all likely various other locations around the world), and even if there aren’t, 47 doesn’t destroy the train or any of the samples on it. So if the train does hold the only copies of all the serum research then it still exists no matter what
But yeah the memory erasing ending doesn’t make a huge load of sense. I just wrote it off as non-canon like the Asylum ending 
I’m more sure Grey had blown it away to make sure they don’t have any copies. Which other reason should he have to blow the building up?
In my head he doesn’t just inject and leave, he kills him after, just using the syringe so the constant won’t die knowing who he is.
If this wasn’t the end of the trilogy I’d say there’s plenty of room for 47’s choice here to bite everyone in the ass but canonically I think this is him in a rare moment of choosing to be a vicious bastard.
This so much once more. Its probably the only contract in the trilogy without any preperations, intel, or group behind you to tell you what to do. Its just you and your target, and I think it really showes what 47 would do with all this freedom of choice and skill. The whole mission showes that, no penalty for nontarget kills for example.
I suspect the idea was that the “cure” was more experimental and only something recently developed in Ether, where the serum was something they just copied from Ortmeyer and probably had in archive.
Also there is the minor detail that unless they kept a sample of the cure in his desk, just in case he changed his mind about dosing 47 - the one person who’d pull the strings that decide whether or not a new batch is made for Arthur Edwards would be his successor.
RIP Janus, the first and last loyal Constant.
Personally I saw this part as 47 being given the option to ‘rise above it’ rather than killing his target as usual and I doubt IOI thought about the possible plot holes related to the serum when they gave the option or cared because they thought it was more effective as a plot device, which I think it was. Killing Edwards would be the easy way out for the Constant and would confirm what he has been trying to convince 47 - that he is just a mindless killer.
Using the serum gave us this alternative option. Like 47 says when he deletes the ICA records and exposes them - “Maybe it’s time for a change”.
If the serum ending is canon it also gives IOI every flexibility to do whatever they want! 
i dunno if i’d see it as the morally superior route. that would imply 47 has moral qualms with killing people, which he most definitely doesn’t. he’s going to carry on doing it, after all.
given the first half of the series has him being manipulated by one group or another, i’d say it’s 47’s sense of agency, of feeling in control of his own destiny (so to speak), that he’s concerned with. he doesn’t want to be just a tool.
i’m still putting my thoughts together on this, but it seems like control and power are the key themes of the woa trilogy. edwards is the face of power in the series.
what 47 does by spiking him with the amnesia-juice is resist power (by not physically killing edwards as he wants/expects) and then ‘kills’ that power (‘knowledge is power’ and all that).
it’s a ‘fate worse than death’.
instead of dying not knowing who he is, edwards has to live with it, and as grey said regarding janus (something like) “death is too easy” for him.
Ye that’s what I meant to add in there. Like you said, this part with the Constant specifically is more about him being in control of his own destiny than whether he thinks it is morally right or wrong. I think rise above it was the wrong term. What I should’ve said is ‘not allow himself to be controlled anymore’ so I probably should’ve said broke the chains or let himself off the leash or something like that ha. He’s not just going to kill because he is told to anymore.
Edwards offers himself to be killed by 47 so 47 is like - fuck you, take this then. It feels similar to the game ‘Dishonored’ where you get the choice to kill your target or to non lethally deal with them, usually in ways which are, as you said much worse than death, but thoroughly deserved.
Its also about using his super power against him.
Thanks to all the protocols in place to erase his past, Arthur will never find out who he was.
I never thought about this. Damn, this is devious.
that’s a damn good shout.
This alone makes it better than killing him. A powerfull guy like Edwards would take death over losing his power any day.
He won’t, but one shouldn’t risk on that in any chance. It would be more reliable if he killed him though
unless i’m missing something, that seems like an assumption without any basis. is there any point in the story where we’re shown/told/given a hint that edwards took some kind of vaccine prior to that scene…?
So what happened with the people on the train? Did 47 kill them all?
Canonically, he probably didn’t. Remember he detatched the wagons and continued the ride with only the constant remaining. They probably found Edwards later. Dead or alive.