It would have been a lot closer, but PS1 still would have won imo. PS1 ~80-85m, N64 ~55-60m.
Not a chance in hell a system with
Mario 64, GoldenEye, Final Fantasy VII, VIII, IX, Zelda: OoT, Star Wars titles, Dragon Quest VII, Parasite Eve, Mario Kart 64, Banjo-Kazooie, Perfect Dark exclusive, plus many multiplats like Resident Evil 1-3, probably Metal Gear Solid, Castlevania, etc. is only selling 55-60 million units IMO.
That's way too low.
They would dominate Japan for one and take the US probably too, which makes it impossible for any developer to keep their game off the system (like Konami and Metal Gear Solid) and they would get the same EA support and all that stuff too.