Tremor had a background. He was a Lin Kuei warrior who abandoned the clan and joined the Black Dragon. Supposedly after Special Forces he was found by the Lin Kuei and assassinated for abandoning the clan, but I don't know if that was ever really confirmed.
I think if any characters get automated by Sektor's Tekunin it should be this guy.
I made up a story for Tasia in my
MK7 thread. To sum up, it involved Sonya (still under Onaga's control) helping him destroy the Special Forces; leaving the only survivor, Gemini (another MK:SF character) to scrounge up anyone she can to help fight Onaga. Tasia, who had been hiding from the Red Dragon, is among her recuits.
Basically Tasia would join Gemini to help destroy Onaga and also hoping getting on the Special Forces' good side would help defend her from the Red Dragon.
Although I very much doubt they'll return since 1) most would probably rather forget MK:SF; and 2) Tremor and Tasia were both ninjas and many feel there are already too many ninjas; I wouldn't mind if they came back. But I'd lose no sleep if they stayed gone or dead.
No-Face I could do without though. Aside from his dumb name, I recall he had a pretty dumb appearence, and if I remember correctly his only attribute was he was an explosives expert with a flame thrower.
And I've expressed my views on Sareena many times.