If you have until you die to repent and recieve Christ, You have until death to repent of that sin
Everyone who is a non believer has blasphemed the spirit. They have taken what the HS says about Christ, His conviction and everything he has done. And rejected it.
As for suicide. If someone gets drunk and goes out and gets behind a car and drives into a tree and gets killed. Is this not any different?
This is not about do we think or know a person is saved or not. Its about the truth
if a person who has eternal life and is born of God given the seal of the spirit commits suicide as a child of God. Does God kick them out of his family (loss of salvation) or does God honor his promise. And they had and continue to have eternal life.
In my view it is Gods character at question here. because salvation is of God, not of us.
As for if, I have a question, if Paul and nicodemus or any ot the others where their and they too said Jesus did these things by satan, Are they still lost. Even though they repented and came to Christ.
Remember, never can be forgiven means that, It can never be forgiven, they would be lost forever, with no hope of repentance..