What role did the Tsaesci people play after Savirien-Chorak was assassinated (marking the end of the Second Empire)? Were they extinct from Tamriel later on?

What kind of lore did the Imperials brought from Akavir when they tried to invade the continent (3E 285)?

They either were bred out of existence, or they were all killed. The people of Tamriel are extremely xenophobic, and it doesn't take much prodding for one group to try and slaughter another.

Perhaps they still live in Rimmen, who knows?

I believe I read that most fled from Cyrodiil, and many of the Teseci finding their way to Elswyre. In fact, I believe Rimmen is where they indeed up.

edit: Ya, what DarkRalen said heh

Considering the khajiit usually give less than two [censored] on what goes on, probably because they're stoned, I can see that.

Those are some wise cats.