Have you tried to use the link over here?: https://etheria.fandom.com/wiki/Mod_Downloads#Conquest_Campaign
Extracting it over the original campaign files in the WBC3 folder should work.
Infinite Interactive is developing Puzzle Quest 3 these days. I once thought that they were raising money for WBC4 or Warlords 5, but I don't think that's the case anymore. PQ3 is what they do now, it's the studio's next big break. Steve Fawkner has been known to leap from genre to genre, depending on the times, and RTS games are too unprofitable these days. Not many of them have a strong following and the playerbase is small. Also the community is far too divided; there are those who prefer WBC1 or WBC2 or WBC3 or WBC3 with the unofficial patches or TPC - and each of these subgroups perceive the games in different ways, from chiefly an RTS game or RPG game to sandbox. There are also those who want any sequel to be identical to a previous WBC game and those who want something more modern and/or new.
It's not necessarily that WBC4 can't be funded, it's that, in the eyes of the entire WBC community, it can't exist. WBC was too amorphous for anyone to have a clear definition of what it was, which will be muddied even further by nostalgia, which any sequel will have to contend with. Just like there's no way of incorporating multiple different visions of the game in a single sequel, there's likewise no way of uniting the fanbase.