Yeah, I know. Extinct. This really depends on exactly when that outbreak of the flu was prior to the start of ESO's story. I saw one comment mention as early as 40 years prior, in which case, no. But I generally seem to see about 10 years prior, which would be totally doable. A common effect of some plagues ( I believe this was common with smallpox for example) is sterility. If the few survivors of the Knahaten Flu became sterile, the only comment you'd see by ESIII's time would be that the flu wiped out the race, just as it does. There wouldn't be any real mention that some lived a full lifespan after. What would that be compared to 700-1000 years? As far as NPC reactions, I would expect any notice of them to be along the lines of "Isn't that a Lilmothiit?" "Yeah. Poor guy."
@Silverwillow, if we're talking about one of the single player games, set in the Fourth Era; uncorrupted Falmer would not surprise me as a new racial pick. There's a bit of throwaway dialog about the Curate looking for more of his people lurking in hidden enclaves somewhere. So, it wouldn't surprise me if Bethesda decided to play with that.
Adding Maomer to TES6 is certainly possible, especially if it's set anywhere in the south.
As to ESO adding new races? If they were to do an Akavir release, I could see the four races from there being added as playable. But, that's a big if. I doubt we'll see Maomer getting added to ESO. It's possible, but it'd be an awkward fit. Maybe if we got their landmass as a playable expansion, but again, that's a big if (though not as big as getting Akavir).
Aren't there any other human races than the three we have?
Ha if Lady Laurent is the authority on the Limothiit being extinct that leads me to believe there are thousands still alive but in areas barren of treasures to steal.