Suppose he had died. Effect on art history? Probably not much. He had already painted the famous surrealist dreamscapes which were to be his most influential work. But in recent years his later "classical" and religious works, once generally despised by critics, have undergone a reevaluation: see https://www.research.manchester.ac.uk/portal/files/63517393/surrealism_issue_9.pdf for example. ("As North American art history and theory move further away from modernist paradigms largely defined by Greenbergian formalism and Breton-style ethics, the later work Dalí produced which had been quietly written off as embarrassingly reductive, commercial and gauche, begins to look surprisingly vanguard.")
De Chirico lived until 1978, only a decade less than Dali, but never attained the same public profile, and is now mostly remembered by connosseuirs and academics(though I personally am neither, just a guy who took an art history class at university).
If Dali dies in 1936, then he doesn't become a huge celebrity in jet-age USA, never gets contracts with Hitchcock and the Catholic Church, doesn't have his notorious summit with Alice Cooper etc. So I think he'd probably be remrmbered in the same way as De Chirico, interesting surrealist artist, definitely had his own vision, but not someone whose name is rolling off everyone's tongue at suburban cocktail parties.
Which might not be an entirely bad thing for his reputation. Without his commissions from the Church, his views on religion are probably connected more closely with his Bunuel collaborations (featuring, among other things, Jesus emerging from a sex orgy) which might belp maintain a stronger image of Dali as a political progressive. And it was during the last two-thirds of his career that he really developed the reputation for being a money-grubbing hack, so if he dies in the 1930s, he might be better remembered for artistic integrity.
(Though I personally am quite glad that he lived to illustrate his Bible, in a more abstract style that was a big departure from his usual. Duckduckgo "Dali Bible".)
TL/DR: Dali dying in 1936 gives him a lower profile, but also a better reputation among those who do remember him.