Whether you've "used the term OSAS" or not, that's obviously what you believe. Also, although it's true that God doesn't go back on His promises, we can STOP BELIEVING and therefore fail to inherit the promises. Yes, we need to PATIENTLY ENDURE UNTO THE END in order to OBTAIN THE PROMISES:
"And we desire that every one of you do shew the same diligence to the full assurance of hope unto the end: That ye be not slothful, but followers of them who through faith and patience inherit the promises." (Hebrews 6:11-12)
Again:
"Cast not away therefore your confidence, which hath great recompence of reward. For ye have need of patience, that, after ye have done the will of God, ye might receive the promise." (Hebrews 10:35-36)
Like it or not, we need to "show diligence to the full assurance of hope UNTO THE END" that "through faith and patience" we might "inherit the promises" and, like it or not, we can "cast away our confidence" thereby never "receiving the promises".