It is one of the reasons we know that Paul wasn't preaching that doctrine. He couldn't have even been forgiven under it!
Not all blasphemy is blasphemy against the Holy Spirit.
Paul says, "But now you yourselves are to put off all these: anger, wrath, malice, blasphemy, filthy language out of your mouth."
(Colossians 3:8 NKJV)
A person can't blaspheme the Holy Spirit and yet be converted by the Holy Spirit.
But anyway, death wipes out all sin. They will have their day to be converted.