There's a concept in biology called "convergent evolution" which basically boils down to, life forms in similar environments tend to independently evolve similar traits.
When Blackmoor D&D was born, Venn diagram of wargamers and fantasy readers strongly resembled a circle. So even if you went back in time and killed baby Dave Arneson and baby Gary Gygax (after you made a quick detour to kill baby Hitler), TTRPGs would've been invented anyway, most likely by wargamers. Some of the grandfathered oddities like Armor Class might not have been invented, but over time, things like THAC0* and the weird saving throws got dropped, and rituals were added, so the evolved form might not differ much from 5E. Because, convergent evolution.
Case in point, legend has it Gygax did NOT want Tolkien references in D&D. But his fans insisted on it, so things like hobbits and ents and elves made it into AD&D, and the Tolkien estate promptly demanded they be renamed, so we got halflings and treants and elves (OK I guess they got away with that one). Because Tolkien was popular. So any "first" TTRPG likely would've had elves in it, because D&D was in fact the game that tried to not have them, and it happened anyway.
So this may come off as a cop-out answer, but it would've been invented, and have significant similarities to D&D. What we can't know is what quirks we'd still be stuck with fifty years later.
*Honestly, this is more of a historical oddity to me than the invention itself: why did THAC0 get dropped, but AC persevered?