But if someone sells campaigns under TDM, wouldn't it be illegal since you're not allowed to make a profit from id's engine?

I really have no idea. I just think that it's more likely than TDM itself getting sold.

Go and try out this mission if you haven't already. It's ... It's just amazing. Most of the guards behave a bit erraticaly and don't seem to have fixed patrol paths (one guard walks around the upper level and then all of the sudden decides to go downstairs to grab food in kitchen! Yeah, they probably do have fixed patrol paths, but those are incredibly well made,) entire mission is incredibly open, with a lot of stuff to explore, tons of different notes and books to add backstory and flavour... It's just fantastic. I'm probably liking it more than A Score To Settle that I've finished yesterday.

Downloaded yesterday, but haven't had the time to play. Maybe after Project Giana :>