Mary Macdonald
Technically speaking, Mary Elizabeth Macdonald did not die in the spring of 1982, but Mary was gone, and none of the others would ever hear from her again.
Technically speaking, Marlene did save the love of her life that summer day 2 years before, but in the end, there was no one left to save Mary from herself.
She couldn't have told you what made her decide to do it, other than that she was all alone, and tired of fighting.
Marlene, her love, her would have been wife, had died in her arms two years before, the second anniversary of her death was coming up in a month or so.
Lily and James, the most optimistic, lively, happy people she had ever known, were dead.
Sirius, who had spent his entire life proving that he was not like his parents, had proved to be exactly like them.
Peter was dead.
Remus was off somewhere drinking himself into oblivion, she had tried to reach out, he had sent her away.
She was all alone and she just couldn't take it.
She couldn't even explain why she didn't just kill herself, other than that it seemed like an insult to her friends who had gone out fighting.
So on that spring day in 1982, when she was 22 years old, she sat down on the lawn in the sun, and wiped her own memory.
At least this way, there was still a chance that someone could bring her back.
But no one ever did, and Mary never found out that Sirius was innocent, she never saw how Remus came back to life. She never found out what Peter did. She never saw who Harry would become.
But it didn't matter, they'll all die in the end.