That's only if one believes something has to be represented mechanically for it to exist in-world. Which is the discussion we are all having. Some say yes, others say no.One can argue that species do not need to be represented by rules at all, but currently they are removing them from the game.
Gold dwarves used to be represented mechanically in 5E14 (via the Hill Dwarf sub-race). Now they are not. Did all of them suddenly disappear from Faerun? Or does one just instead state that within the fiction of the Forgotten Realms that certain characters are gold dwarves as opposed to shield dwarves?
And what about tabaxi? Did they exist as a people in D&D before they had a species mechanic given to them? Or was it only after Volo's Guide to Monsters came out did they suddenly just show up in all the different settings by popping into existence?
It's this idea that some people are making that something only exists in the game IF there is a mechanic for it that I push against. Because there are thousands of things that exist in D&D that do not have mechanics-- or more specifically-- do not have mechanics as produced by Wizards of the Coast. So saying it is a necessity for the game on the whole is just not true.
Would some people find it lovely to have half-elf mechanics in 5E24 as produced by WotC? Sure. But do they HAVE to have them? Of course not. Because they can either bring forward the species from 5E14 if they need it, or from any other 3rd party producer of D&D material that might have already made a 5E24 half-elf. Or even one that they made themselves.
At the end of the day... WotC may end up producing a half-elf statblock at some point. And so people will get what they ultimately wanted. And that's cool. But that's how it is with all game mechanics... you make due without them when they don't exist and then you choose to use them when they do.