I put "necessary" in quotes for a reason. I am implying more or a marketing and distribution form.You're not talking about the existence of Beyond, you're talking about Beyond being "necessary" to play in some sense. The current game is exceedingly far from requiring something like Beyond to play, so I can't envision a world in which a backward compatible version of the game changed it sufficiently such that you could reasonably say that Beyond was needed to play it.
For example: what happens if they move DMsGuild to Beyond? Or, what happens if they pull VTT licenses? That sort of thing.