While we have yet to see the final 2024 rules . . . I'll bet you 100 gold pieces that you will be able to make a "half-elf" with the new rules. Or rather, a character with mixed human and elven ancestry. It probably won't be called a "half-elf" and the game rules will likely be different . . . but it will be there. Same with the half-orc, although that is less popular a choice.
I'm fully expecting a sidebar talking about the issue with "half" races, specifically calling out the legacy PC options of half-elf and half-orc and guiding players on how to realize those archetypes with the new rules.
Will this change incite riots, cost WotC sales, and destroy D&D as we know it? Nope. It will be fine. Will folks grumble on the internet over the change? Of course, that's fandom!
We'll see how they handle it.
Where I agree is that there are ways they can handle it safely. I think we even broadly agree on what way that is:
A) Have a system in-place, in the PHB, for mixed species, which gives them a mixture of the abilities of their parents.
B) Specifically call out Half-Elves, hopefully without ridiculous beating-about-the-bush, name-wise, and explain how to make them.
C) Have the mixed species rules not result in something which obviously inferior, mechanically, to humans and elves (it's probably fine if it's arguably superior).
If they do all of that, and do it reasonably well, I think they'll be okay on that particular point. I think if they ban purchases of 2014 instantly when 2024 comes out, they will still face fierce backlash, because there will be people who wanted the classes etc. from 2014 (or at least thought they did, it makes no difference). My feeling is that's really 50/50 whether WotC actually understands this, given their incredible number of slip-ups, most of them trivially avoidable, over the last few years.
On the other hand, 67% of people in
the thread discussing Half-Elves disagree with you and think WotC won't do that (how did you vote?). They apparently think WotC will just go ahead with the extant "you are only one race
really" hybrid rules. If they're right, absolutely this will cause lost sales and incite "riots" in the online sense. Destroy D&D as we know it? No-one has suggested that, but it'll cause a schism. Multiple schisms probably, and give a big boost to any 5E alternative using a less obnoxious/racist system - which is probably all of them (certainly A5E).
I mean, this is ironically a big test of how well WotC understands their actual playerbase, including their most devoted players.
Anyone who knows the broader D&D community know that very special snowflake (I say that with love, having played similar on occasion), unusual-parentage mixed characters are extremely common and popular with a lot of D&D players, especially those who create or pay for fan art of their characters and so on. This has always annoyed the most extreme traditionalists (who basically think everyone should be a Human Fighter or Elf Wizard anyway, or at the most extreme, perhaps a Dwarf Cleric or Halfling Thief), but the half-dragon-half-demon-half-elemental-half-cat people have existed since at least 2E (I can't say further back because the internet didn't exist). WotC, if they understood their audience in the least, should absolutely be embracing these people. They're precisely the sort of people who are highly invested in D&D, both mentally and often financially (you know someone who is willing to drop $200 on a character portrait is buying almost every book that comes out).
But the first thing we saw in 1D&D/2024 was a big middle-finger from WotC pointed exactly at those people (and pretty much everyone on the planet of mixed heritage), with their "Nah just pick one race" approach. How many people approved that? How many people said "Yeah that seems like a smart idea!", because I'm guess it was at least a couple of handfuls, and if WotC was remotely in-touch, that couldn't happen.
You think that, despite all WotC's screw-ups, they will definitely get this right. You might be correct, but you'll well-advised in betting low values of fictional money, not really money, because I don't think the odds are that great. Apparently nobody else does either given the voting in the linked thread (I actually voted that they will have a crunchier set of options, but I'm a bit of an optimist, I guess).