Who said you can be out of fellowship with God and still be saved? I'm an OSAS proponent, as you called us, but I don't recall ever saying that you can be out of fellowship with God and still be saved. I do recall saying that once you are in Fellowship with God, once you know Him and are one of His, that He will never leave nor forsake you, which means you are saved forever. But then, that's what God said also. You can never get out of fellowship once you are in.
That verse in Mathew 7 that you noted says, "I never knew you. Depart from me ye that work iniquity." He never knew them in the first place, which means they never got saved in the first place. It's not talking about people who are saved, then losing their Salvation over some sin they committed.
It's talking about people who try to get into Heaven some other way than through Jesus. More specifically it's about people who think that their own almighty good works and righteous acts cause them to deserve heaven. They depended on their own righteous ability to do good and be good and obedient, instead of on the Lord's grace, love and mercy to save them.
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Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
To depend solely on the Lord for your Salvation instead of yourself you have to be an "OSAS Proponent".