Or the elf player can instead play at a different table where elves are part of the setting. That way everyone gets exactly what they want!
Rather bold of you to assume such a table
exists. Which is the whole problem here, I think. Many, many, many, many (to the Nth power) times, there is
one game on offer. Or there is
one game a person can make time for, or which is run by people they know (and thus they are actually comfortable playing in it), or...etc. It's real easy to dismiss legitimate concerns with "oh just
find a table that does what you like!" without actually factoring in that that can be
very difficult.
I've tried searching for a game, scoured multiple forums, even managed to get one game together by hyping up people from three different forums (which, sadly, fell through after the first adventure ended.) That game was the
one success I had at finding a 4e game after the long-runner I was in had to fold due to sudden
massive lifestyle changes our DM had to make.
One success. Three
years of looking. You may understand, now, why I take such a dim view of blithe "oh just find a game that suits you!" responses.
Edit: And the assertion from your previous post is simply false. You do not
need to establish those things. They can be allowed to grow up organically in whatever ways make sense. As Dungeon World puts it,
draw maps, leave blanks, just in this case the "map" is the list of known sophont species and the "blank" is about something beyond the horizon or the like.
The only DM who
needs to establish such things is one who demands unilateral control over the contents of the narrative space: "You can tell any story you want, so long as you only use the newspaper clippings I permit you to have."
"I don't like meat, so I'm just serving tomato and lettuce on hamburger buns."
"Uh...couldn't you...at least have a veggie burger or something?"
"Why?"
That's how your question comes across to me. Simply deleting something which serves a key, foundational part of an expected experience--removing without replacing--is likely to lead to an impoverished experience. Of course, what qualifies as "foundational" is subjective. For some, if there aren't always-evil orcs, it's not D&D. For some, if there
are always-evil orcs, it's not D&D. But there is, at least loosely, a general understanding of what must thematically be present in something called "D&D." Axing elves, and doing nothing whatsoever to fill their "magical, aloof humanoid" niche is likely to leave players dissatisfied unless you get their enthusiastic buy-in for such a premise.
Popularity and tradition are useful guides here. Dragonborn, for example, are not
traditional but they are (at least based on substantial data sets from active characters on D&D Beyond) popular and growing in popularity. A game that lacks them might be totally kosher for one group, and verboten for another. By comparison, drow technically have quite a long pedigree but are...shall we say, a
selective taste, really loved by the fans and not particularly cared that much about by the non-fans. Missing drow in a game may simply never come up as a relevant issue. You also have things like settings that use an absence as a conceit: dragons are rare to unknown in Al-Qadim, there are no divine classes (and there have been multiple exterminated races) in Dark Sun, Eberron is specifically designed to be pulpy action-adventure fantasy kitchen sink, etc. Egregiously breaking those patterns can lead to problems.