Personally, I think it would have improved his legacy, since it would have butterflied away the scandals of his later years (the infamous pee and fart tape, the time he was arrested for hiding cameras in the ladies room, the time his nudes were published in a tabloid)
I don’t think it would have, however, turned him into a Lennonesque martyr figure, since Berry’s music wasn’t deep and philosophical like Lennon’s was. He would probably be remembered like Glenn Miller or some other talented artist who died young.