When i play Civ3C i always try to eliminate all of my opponents. But as i'm not one of the best Civ-players in the world, i never end the game before 2050 or whenever the game ends.

Now - I have this feeling that when i reached 2050, the game changed from the second easiest dif to Chieftain since i didn't win the game after year 2050. Am i wrong on this one, or can it be true that the dif changed back to an easier level if you don't win (like one of my opponents suggests i go back to chieftain)..

I would like to play this game until either i'm destroyed or until i have destroyed all of my opponents, but i would really hate if the game automatically goes back to the easiest dif without asking me whether i want to do that or not...

Must say that i might suspect myself from choosing Chieftain at the beginning of the game, but don't really remember

you mean when you continue playing civ after 2050? afaik, it doesn't change. it hasn't done to me though.