Looking at the passage below, it seems to describe a “win-win” situation, so “safe bet” seems closest.
“A sensible person reflects on this matter in this way: ‘If there is effective action, when this individual’s body breaks up, after death, they will be reborn in a good place, a heavenly realm. But let’s assume that those who say that there is no effective action are correct. Regardless, that individual is still praised by sensible people in the present life as being a moral individual of right view, who affirms the efficacy of action.’ So if there really is effective action, they win on both counts. For they are praised by sensible people in the present life, and when their body breaks up, after death, they will be reborn in a good place, a heavenly realm. They have rightly undertaken this guaranteed teaching in such a way that it encompasses the positive outcomes of both sides, leaving out the unskillful premise.”
Yes, I agree, “safe bet” or “win-win” are pretty good, indeed I tried to translate it as “win-win”. But as so often, a more idiomatic rendering, while attractive, didn’t quite fit in the different ways the word was used. I think “guaranteed” is quite good, though!