Well as far as i know multiplayer campaign isn't possible... and to load a hero in next map use game cache (if it's possible the multiplayer you should prob use save/load system of any kind but it needs to be heavely edited)
It could be possible with multiple maps using the same heroes, items, save/load codes, etc., but that seems much too ambitious for a wc3 map.
Besides that, it would be incredibly annoying to have to host a different map every time you want to advance the story. There'd also be problems with people that haven't played the game joining a map that's supposed to be played only by high level players.
I'd say it's technically possible to do, but it'd probably be easier to just try to pack everything into a single map.
I saw once in an ORPG map i played long ago. You play the map reach lvl 30 max in that map and than you save your hero and play the second map. When you enter the second map it automaticly asks you for the load code. If you dont have it, the map ends (DEFEAT). So you could play only if you have the code from the previous map.
If you have it than you continue your story. With what weapons you had before and stuff.
if someone knows how to do this and wants to help. I will greatly appreciate it.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.