Why is everyone certain Regulus is a dead deserter?
Ok, so this seems like a dumb question: it's because he is a dead deserter, Leo. First of all, no he's not, he's alive and well. Sure, but there’s no reason for anyone to be privy to that information pre-DH. Literally the only person who knows that Regulus is dead is a house elf with orders to keep it zipped. So it’s weird when Remus says this in HBP:
“And they’ve found Igor Karkaroff’s body in a shack up north. The Dark Mark had been set over it — well, frankly, I’m surprised he stayed alive for even a year after deserting the Death Eaters; Sirius’s brother, Regulus, only managed a few days as far as I can remember.”
It’s an offhanded comment, and from a meta perspective, it’s clear why we’re being reminded about Sirius’ dead Death Eater deserter brother. But it’s oddly specific and implies that Remus is recalling two separate days, one in which Regulus deserted the Death Eaters and one in which he was pronounced dead. Which really makes no sense. So where is this coming from?
He’s likely just repeating rumors and assumptions. I imagine there were plenty of them flying around in the first Wizarding War. This line is also taken from a really dismal piece of dialogue in which Remus is pessimistic af about the war. It could just be a sort of, “Voldemort kills all his deserters and enemies with a quickness rip” fear based comment. And he’s almost certainly repeating what Sirius has told him about Regulus’ death, because Sirius has the same narrative for Harry in OotP (he joined, he deserted, he was killed).
That’s an unsatisfying answer though. Because again, it’s an oddly specific narrative and it’s delivered as though it were fact by Remus, whose only uncertainty seems to be whether he’s remembering the length of time Regulus stayed alive correctly or not. Which--he isn’t. But more on that later.
Sirius doesn’t deliver his version of this narrative like fact; although he clearly believes it to be true, he is upfront about it being vague, secondhand information:
“From what I found out after he died, he got in so far, then panicked about what he was being asked to do and tried to back out. Well, you don’t just hand in your resignation to Voldemort. It’s a lifetime of service or death.”
But who tf told Sirius this, and where did they get their info from?
The reason Sirius is sure Regulus is dead in OotP is clear: the tapestry. There is definitively a date of death on the tapestry for Regulus. That’s how we get this exchange between Sirius and Harry, King of Tact:
“He was younger than me,” said Sirius, “and a much better son, as I was constantly reminded.”
“But he died,” said Harry.
Well spotted, Harry. Very compassionately put. Yes, he died. So says the tapestry. But where did that death date come from?
There’s fanon about the tapestry being magical in a similar way to Molly Weasley’s clock, where it just updates with births and deaths. It makes sense that it would, but if it does, that baffles me even more. Here’s why: Regulus’ mother doesn’t seem to know that he’s dead in the aftermath of the cave. Kreacher tells us in DH (emphasis mine):
“And his mistress was mad with grief, because Master Regulus had disappeared, and Kreacher could not tell her what had happened...”
Walburga is distressed over her son’s disappearance, not death. If the tapestry updated with death dates, it would have updated when he died in the cave and Walburga would have known, at least, that he was dead. Maybe the tapestry is magic, and it escapes her notice. But wouldn’t that be the very first place a mother would look when her child, who is in a violent gang in the middle of a war, suddenly goes missing: the tapestry that could tell her if he’s alive or dead?
But if the tapestry isn’t magic, then the only way a death date got there is if Walburga updated the tapestry herself, which then leads to “why is Walburga certain Regulus is dead?” What convinces her to do this? Unclear.
Whether the tapestry updates itself or Walburga updates it, though, it leads to the same result: Regulus died the day that he disappeared. He rolled into Grimmauld, picked up his house elf, went to the lake, and died day of. So the date that magic omniscience would put as the date of death and the date that Walburga would associate with the loss of Regulus would be the same.
So...where is this “he deserted and then died a few days later” narrative coming from??? There were 0 days where Regulus was on the run from Voldemort. Regulus yeeted himself into a lake of corpses rather than deal with the fallout of deserting. Who is out there saying he pulled a Karkaroff and tried to hide?
And again, why does everyone seem so aware that Regulus backed out of the Death Eaters at all? How did that become common knowledge? Regulus made a point of not telling anyone he was betraying Voldemort, Hermione notes in DH that he didn’t even explain that to Kreacher. But somehow everybody knows or assumes this is the case? Is he really bad at keeping his cover or is the Order just like “well, it wasn’t one of us, so he must have pissed off his own people”?
And I just don’t understand why more people weren’t like, “he’s missing, he’s almost definitely dead, but for all we know he’s still out there somewhere”. Because before DH came out, Regulus Lives wasn’t an AU, it could very easily be canon compliant. Kreacher is the only witness who could confirm Regulus’ death, and he didn’t until he told the trio in DH. All we had was that tapestry saying he was dead, and are we really trusting some dusty old moth eaten thing that doesn’t even have Sirius on it?? I guess we are. I guess we are.