Your husband can come back, with a sacramental confession, any time.
I don't know what thet priest really said. He might have been misinformed, misunderstood, or he might have referred to some unusual circumstances under Canon Law, when a sacramental confession is impossible and death is imminent.
I think that's the point. Forgiveness through Christ's atonement isn't confusing, oblique, uncertain, ill-defined, or circumstantial. It is black and white. Either Christ died so that you and I and all God's children would stand before God acquitted of our sins, or He didn't.
I believe He did, as Christ has assured us in Scripture.
I know your offer is sincere, but a day does not dawn that my husband does not thank God for his faith and for the assurance he and his family have received by the certain knowledge of Christ's redemption of us.
It's a gift.