Well a genuine Christian will keep on believing that Christ died for his sins according to the Scriptures, and rose again for his justification according to the Scriptures. Children of God will also be kept by the power of God. So that is really a non-issue.I agree, the osas doctrine is a man-made falsehood.. Your only saved if you keep believing, and your only saved if your not a hypocrite.
As to not being saved if one is a hypocrite, if you mean by that people making a false profession of faith, then of course they were never saved to begin with. But there is an instance recorded in Scripture where Peter seemed to be a hypocrite and was rebuke by Paul (Gal 2:11-14). No one would dare say that Peter became "unsaved" at that point, and then suddenly recovered his salvation.
The reason many Christians cannot bring themselves to believe in the eternal security of the believer (commonly called OSAS) is because (1) they do not see salvation from God's viewpoint and (2) they do not fully grasp the fulness of salvation, and the many facets of salvation, which prevent any Christian from losing their salvation.
The fact that God predestines believers for glorification is sufficient proof of the eternal security of the believers. Study Romans 8. Salvation is of the LORD.
For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren. Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified.