If that happens, players will simply lose interest. After all, that's the most important thing in an expedition, isn't it? You could create bots and make them fight; it wouldn't change the meaning.
Bots are something completely different. This way, you have your own character, with their own story, motivation... You have complete control over the combat part of your character, determining their tactics, actions...
For example, you could develop a complex combat mechanic in turn-based mode, where you need to find the enemy's weak spot and crush it, otherwise you won't win.
I'm not sure it will work. You could try implementing PvP or Competitive matches between teams of players to see who is more successful in the arena, but I don't know...
In my opinion, Dal Shabet, for example, was successful because many players and GMs were involved, and practically around the clock. There was almost no long wait for a response from the GM or player. That's why it turned out so great. But interest is lost when you have to wait a long time for a response. So, it's more about the ability of players and the GM to spend a lot of time playing, rather than the specifics of the game's implementation.
Well, I don't know. In my opinion, a forum based solely on battles won't last long. However, it depends on the implementation. Also, it would be desirable for players to gather at the same time, otherwise we will be waiting half a day for a response, and interest will quickly fade. But it's worth a try.