More like 10-11. They wouldn't have gotten 6 seconds run off on a play that was essentially "run a few yards backwards into the end zone and don't lose the ball"
Still, a FG attempt wasn't on the table. Suppose they only got the clock down to 10 seconds. Even if the 49ers just kicked the free kick out of bounds, with no timeouts, there is no way the Falcons get into range and get the clock stopped. No matter what, the game was going to end with the Falcons heaving the ball into the endzone for the win. All an intentional safety does is take the potential for a blocked kick being recovered for a TD off the table. The more I think about, it still might have been the least risky option.