In most cases you have the right to emulate if you own the original game or a licence to play it (so if you have it on Steam you technically can).

Otherwise, sailvthe high seas at your own risks, but law won’t be on your side.

Note : my own opinion is that as soon as tge game isn’t distributed anymore, you have to right (sometime the duty) to emulate, even it it means pirating it. But that’s only my opinion 😉.