Just how "Extinct" are the Extinct Races?

[SonTao]

By this, I mean realistically how many Saiyans, Namekians, etc survived their initial purges/catastrophes/whatever. We know Frieza has completely annihilated various worlds such as Planet Vegeta--but it's clear he's absorbed their species into his workforce. But aside from that, do you think there are stragglers floating out amongst the stars? There's damn well going to be another Saiyan down the road, they're like cockroaches. But what about the Namekians, Ginyu's race, or Paikuhan's people?

[Hellspawn28]

It's possible that other Saiyans from Sadala in U7 that could exist. Living low to avoid other people from finding them.

[Magnificent Ponta]

The Granolah Arc of the Dragon Ball Super manga established that Namekians have always been scattered throughout the Universe in small enclaves on various planets; though it's unknown how many survive, it's not unlikely that several small societies (apart from the "main" one on New Namek) survive.

[Makaioshin]

Saiyans and Namekians are the only two from the ones you named that come close to that idea in the original work. Namekians not so much now with that idea that they came from another realm entirely. Tsufruians are another one and those stories just work off the baseline they were wiped out entirely.

As for the others you named, we are only introduced to those characters as individuals without a focus on their races. So there is no reason to think their races are endangered to begin with. There are some answers in games though that is far from the main story like the Freeza Clan in XV or other Ginyu enemies in the Freeza Army with the RPGs. In Shin Budokai, Paikuhan is offered the chance to return to life and comments that he is fine just continuing to visit his hometown every year. So that seems to imply they are fine.