It has been posited, in so many words that aren't exact to those I'm using, that there is a differing measures of God's grace. It seems some are given a steak dinner while others only get peanut butter sandwiches. Or everybody gets peanut butter sandwiches, but only some are offered the steak dinner. It is my view that the steak dinner is offered to everyone but some stop short of submitting to the dress code and settle for peanut butter sandwiches.
It is also my view that the natural man is as dead as the spirit man, and vise versa, as that is the sure prognosis. The man, as a whole, is deathly sick and in dire deed of a physician. He can do nothing to either heal nor help deliver himself from that certain end. But, there IS help for him, the Great Physician that is so equipped that He is able to raise anyone from death, as He has proved naturally so that all could see and just as skilled at raising the spiritually dead, and coming to Him is indeed effectually confessing our sickness unto death. My view is not that far of a throw from your view, short of the 100 percent anything. I mean, 1 percent alive is quite really dead, physically, so I can't rule out that spiritual death doesn't operate in a similar manner. So, I can go so far as accepting that a man can be born .01 percent spiritually alive and in grave danger of complete death even if his body is 99.99 percent alive, but I can't rule out that that .01 percent of him (the only part that can hear the Spirit) cannot, somehow, with the help of the Word of God, eventually overpower his nature to live as a complete animal.
It is of my opinion that is never too late until one is completely dead dead dead.