Probably plenty of players giving D4 a try. I don’t think D2 or D2r are killable by a new Diablo game.
D2r nowadays is such a niche game, that it is only played by hardcore D2r fans anyways. The biggest drop in D2r came after peopel who did not play D2 before or not in a long time, decided to quite the game after a few months, to avoid death by boredom.
D2r is not a game that is appealing to a wide audience, therefore not much to lose by D4 quite frankly.