I have always understood that this prophecy referred to Mary's grief at the crucifixion of her beloved son; that is, it is an indirect reference to Jesus' death. If so, it was fulfilled when Mary (John 19:25). Further, while Mary Magdalene was crying at the Jesus' tomb on Sunday morning, I am confident that Jesus Mother was just as grief stricken, if not more so. It is in this sense that her soul was "pierced". (As pointed out by Nigel J, a sword (rhomphaia - large Thracian sword) can only pierce the flesh.) Compare 1 Tim 6:10 for a similar idea (but for different reason).
Further, this prophecy of Simeon appears to echo those of Isaiah 52:14 and 53:12 of the suffering servant and so become the earliest NT prophecy of Jesus' suffering and death.
I am unaware how Mary met her death, but tradition suggests that John, who became bishop of Ephesus adopted he as his mother and she presumably lived there. However, I do not know if her death was natural or homocide. I suspect the former.