What's so frustraing about that 1981 game is that Dallas dominated it, forced six turnovers, and if you watch that final drive its really anti-climactic and not as dramatic as commentators make it out to be.
Even after all that Dallas almost pulled off a miracle comeback to put them in field goal range, now that truly would've been memorable to win with 54 seconds left as opposed to having five plus minutes to execute a drive.
The real story of that game is penalties that stall Dallas drives, the Niners were lucky to win and were dominated in the trenchs all afternoon.