hi everybody, I think I have completed all the quests, but if I'm not wrong last time I finished the game there was a message 'officially stating' that the expansion was complete. If I look at the diary I still have 1 mission about Mendas and Balduran, it's just the info that Dushai tells you, but I have the impression I missed something..Durlag Tower is ok (just killed the demon and came back to the gnome - no reward... - ), before I killed Mendas and his pal and ghe werewolf thing is ok, the first quick mission has been done immediately..did I miss something?
I'm using BGT, so I don't know if it may affect that..I don't even know if completing the questa out of order (I did the werewolf island before durlag tower) may also affect the final message.

There are three quest arcs for TotSC: the Ice Island, the Shipwreck Island and Durlag's Tower. After you complete all three of those, there will be one final quest arc back in Ulgoth's Beard involving some cultists and a demon (this may be a part of Durlag's Tower -- I'm not sure if it's really it's own "thing"). I've always done the quests in that order, and when I kill the demon I get the message that the TotSC is complete. However, I've never used BGT, so I'm not sure if you'll still get the message using that mod.

I'm using BGT, completed Ice Island, then Werewolf Island then Durlag's Tower, came back to Ulgoth's Beard beat the big bad demon (that was a very tough section) but I don't remember getting the 'you've finished TOTSC' message either.
This was my first play-through though so I didn't know much to miss it.

I don't think it shows up in BGT. If memory serves, there's no indication of when you've finished BG2 and are starting ToB. It's just a smooth transition just as if the game's one long seamless adventure. I assume it's the same with BG1/TotSC.