I don’t think it’s reasonable to assume that he could predict the Patronus stopping the curse. Harry didn’t know it could do it. How could Quirrell, who can’t even cast Patronus 2.0?
Additionally, he had to be certain that Harry wouldn’t be able to recall his Patronus, which would also be beyond him.
I think that’s why he cast the killing curse—to get Harry to expend his Patronus.
I don’t think it’s reasonable to assume that he could predict the Patronus stopping the curse. Harry didn’t know it could do it. How could Quirrell, who can’t even cast Patronus 2.0?
Additionally, he had to be certain that Harry wouldn’t be able to recall his Patronus, which would also be beyond him.