An unreasonable and faulty conclusion. Do you dislike JW's so much that you would judge they have no hope at all???
You are taking a far too narrow view, and ignoring plenty of relevant scriptures and the broader scriptural teaching.
It is the redemption value of Christ's death presented to God as a ransom that allows ANYONE to have forgiveness of sins.
His blood is not the new covenant. He said it was the drinking of the Cup which created the New Covenant, which merely symbolises his shed blood which was to be poured out on their behalf. The New Covenant Jesus concluded was for a Kingdom, not for forgiveness of sins. It was with those to be born again of holy spirit to be adopted as heirs, to rule in the heavenly Kingdom. Just because not everyone is in that Covenant doesn't mean they cannot gain the benefit of Christ's having died "..so that EVERYONE exercising faith in him might not be destroyed but have everlasting life."
That means anyone, Jehovah's Witness, adopted as an heir, or not.