A clan as a dying entity.

The idea itself is not outdated. What is outdated is the desire.

I don't think an organization can die out. The game itself is popular, and there are people who enjoy working on it or playing it.
In general, we need to create a system that keeps people interested and keeps the Clans in a state of competition (more on this below).

But gradually, the subculture of each one is simply scattered across the Heroes forums.

But that's great if it's presented nicely. You can ask map creators to indicate on the map that the map is from your Clan, or to create joint maps with several map creators from the Clan. And then there will be something like competition, which may even encourage other Clans to compete for the quality of maps. Well, this leads to various contests for joint map creation by Clans, and so on. I haven't fully fleshed it out, but the idea is clear.

In a normal Clan, people can be very different (player, map creator, organizer, designer, writer...), while others usually simply define a division into groups (there is one caveat: playing Heroes can be a sufficient basis, because this is the main idea).

Yes, that's logical. This can create great synergies. It all comes down to organization again. Here is my subjective vision.