There is a common misunderstanding about the forgiveness of sins. People who smoke dope while quoting Jesus are particularly prone to this misunderstanding, but others have drifted into unorthodox understanding of the forgiveness of sins.
If the person you have wronged dies, or has something irretrievably harmful done to them, you may very well be screwed no matter how "sorry" you say you are, if you waited so long that you either missed the chance or the person has suffered in a way that cannot be re-mediated. In the first case the person has died and so cannot forgive you, and in the second case, they are not obligated to forgive you. You cannot quote the "Our Father" to them and force them to forgive you; God will not stand for that. The Our Father refers to a pattern of a forgiving mind set; it is not a mechanism to force a good Christian who has been grievously wronged to forgive you. There is much in what Jesus said and also in the older scriptures about the need for prompt and thorough remediation of the wrong performed by your sin, and it is only after penance and remediation that forgiveness might take place, both by the person wronged and by God. If you have waited so long that the person has suffered grievously, or God forbid, has died before you repent, there is no Christian obligation to forgive and you may well not be forgiven. If the person who refuses to forgive has led an otherwise forgiving life, then God will not judge them as unforgiving and instead, God will render justice on the wronged person's behalf.