It is true that this fear tempts people to apostasize and wind up either becoming a complete hedonist with whatever time you have left, or trying to find a way to immortality outside of Christ. The thing is, who can overcome God? Nothing but a fiery judgement awaits.
About God not wasting his time drawing those who've blasphemed, are you sure about this? There are temporal consequences and judgements that come on people because of sin, but final judgement hasn't happened yet. What if a person has committed blasphemy of the Holy Spirit, but they continue walking the Christian path afterwards, and then get sentences to hell in the final judgement? Kinda like those who were casting out demons in His name, doing wonderful works in his name, etc., and yet were still workers of iniquity? They weren't cast out into hell immediately; they received the reward of their error at the final judgement.
Would God still use someone who messed up like that for his purposes, like a vessel of wrath fitted for destruction?