Salvation must be understood as a two-part process. Prior to Christ’s atonement, sins could be forgiven, but that alone was not enough to be saved; sins also had to be paid for. The OT saints could have their sins forgiven, but then had to wait in escrow, Abraham’s bosom, for the atonement to be made, paying for their sins before they could be saved, and receive the Spirit of God. Receiving the Spirit was the promise of salvation.
Ezekiel 37:14 And shall put my spirit in you, and ye shall live, and I shall place you in your own land: then shall ye know that I the LORD have spoken it, and performed it, saith the LORD.
Ezekiel 36:27 And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them.
Receiving the Spirit could not happen until Christ’s paid for all sins.
John 7:39 (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)
So to answer your question, the OT saints could not benefit from salvation until the atonement was made, but could have their sins forgiven. Salvation is a two-part process; sins were paid for en-mass, but forgiveness is individual. It does not matter in which order they proceed.
Luke 5:20 And when he saw their faith, he said unto him, Man, thy sins are forgiven thee.
Assuming for the moment that Christ failed to or decided not to offer himself in payment for all sins, then all bets were off; Abraham’s bosom would have emptied into hell.