The "would be" primarily moves the replacement from the initiation to the resolution of the effect. The effect initiates as a kill, so you have the opportunity to save from a kill effect. Then, when the effect resolves, you do something different than usual is done with it.
Also, the basic timing of a Response such as Arya's (which happens after the resolution of another effect is completely done with) and a replacement effect such as The Kindly Man's (which takes place as the resolution of another effect is in process) pretty well calls for a different verb tense. That difference in the timing of action necessarily calls for a different verb tense.
Take this example: A schoolteacher gives her students a test. However, thinking after the fact that it was too hard, the teacher decides that if any student would fail, the grade would be rounded up to a 65 (a passing grade). The teacher scores my test and counts 60 points. Did I fail?
Well, to make this completely analogous, you have to look at a Response to the passing/failing grade, since what we're really concerned with here is how the replaced effect is treated for the sake of which Response effects can be used. Say the school has a policy of "after a student receives a failing grade on a test, they are eligible for a free tutoring session." Are you eligible for free extra help? And what about the students who scored 50 or 40 or 30, who were also bumped up to 65? Are they eligible for the extra help? Whether or not "fail" is written in the teacher's grade book, should they be?