uhhh interesting, cause mostly i picture her surviving in a scenario where they win the war without losing the potters. but…
judging by the letter harry found in sirius bedroom, the mckinnon’s died near harry’s birthday. so between their death and the potters are only a few month apart and in war times there’s no much time to stop and grieve. they are only allow to feel everything and actually process what happened, what they lost, after voldemort gets wiped out.
100% marlene wouldn’t have let sirius do anything stupid. at best she saves him, at worst she joins him. she’s the witness that saves him from imprisonment (she turns to dumbledore who turn to the minister blablabla he gets a fair trial, they win).
so while they trying to help each other in their griefs, because they are so young and haven’t have enough time and space to breath, i don’t think they had fully figured out every aspects of their relationship, meaning they might no be solid enough for them to endure what it means losing everything they once cared of. harry, despite everything, still goes with the durleys for his own protection.
so yeah, i think their worst character traits come to play and they cannot reconcile who they are as individuals let alone as a couple. they care for each other, ofc. in the end i think it their only option if they ever aspired to keep on each other lives.
there are certain things that you can only ever learn on your own. only distance can make understand what happened. they do evolve. they do manage to get their heads above water. and possibly reunite somewhere in the future, maybe with the whole thing of voldemort coming back, harry being in danger. he finally gets two people who knew his parents and are able to tell him all kind of stories he longed to hear.
harry, in the end, brings them together and this time, they make it.
I have so many favorite hc for blackinnon, but my all-time favorite is Sirius having a bad feeling the night Marlene dies and telling her not to go home, to spend the night in his house, to stay together-- but Marlene thinks he is being paranoid and goes to visit her home, and ends up dying there with her family. I just love the idea that Sirius lives with the regret that only if he insisted more, maybe that wouldn't have happened.