By that logic, what then was the sin of the Baptizer? Or that of the holy Apostle-marytrs?
There are many stories in the lives of saints of heretics and persecutors of the Church (Arius springs to mind) who had awful accidental deaths or who "got what they gave" in some treacherous fashion or another.
We pray in the Orthodox Church at every liturgy and at other services for "A Christian ending to our life, painless, blameless and peaceful, and a good defense at the dread judgement seat of Christ."
There are traditions (especially monastic ones) that there is a relationship between the holiness of one's life and the peacefulness of one's death. This is of course not at all an absolute. But we are encouraged each time we see it. Having had the opportunity to observe a few of those peaceful deaths, there is something to it.