That sure SOUNDS pretty complicated. Of course "you either are or you aren't", but if you "ARE" can you later become "AREN'T"? IF "no" then Steven is/was a liar and never believed what he claimed to beleive (and defended quite... um... "aggressively". If "yes" then OSAS is a false dogma.
Can a saved person fall out with God? Sure. I did at one time in my life. People who do though usually do from some crisis that has occurred and are eventually brought back into the fold. Here IMO actions are very important cues. Are they happy or appear lost and searching? If someone was truly saved they will not have peace until they are right with the Father and the Son.