Alright, thank you all for the replies (I was not expecting so many!)
After giving this some thought and reflection as well as reading through your responses, this is the conclusion I have come to:
I believe it is at the moment we come to trust in the work of Christ that we are saved (or justified). But as Apostle Paul says, we are "being saved," which is a continual process. I believe this often works out as God testing and reaffirming our faith. In this way, I believe progressive sanctification is a process of salvation that, without it, we are no more saved than before we put our trust in Christ's work. We may drift away from that trust for a time only for God (Himself) to draw us back into the fold (leaves the 99 to find the 1). As to how much it is God who "Keeps us," I think that is a very complicated topic, and though Christ loses none who come to Him, we can walk away from the faith permanently if, in most cases, we find ourselves in a pattern of sin to which we no longer can (or want to) repent. This is why the Biblical writer says, "test yourselves to see if you are in the faith." Can you humble yourself before God and repent if need be? If you can, you are saved. If you can't do that, I think it is at that point that you have forfeited your salvation (as Christ alludes to blotting out our names in the book of life). But I think just as salvation has a singular point where we trust in Christ's work, we can lose our faith by not trusting in Christ's work which is also a singular point (which cannot be undone). So as far as sanctification is concerned, we are to "be conformed to the image of Christ," and I believe this starts here on earth. Still, as our knowledge of God increases (exponentially) after the final judgment in the NHNE, so to the degree we become more conformed to the image of Christ. It says Christ was perfected here on earth even though he was perfect. I take this to mean when we get our glorified bodies, our journey is amplified, and even though the world will be perfect at that time, we will still grow in holiness for eternity.