I tried it – different monsters are not generated from the same save file. As far as I remember from the original game, the contents of dungeons, magic guilds, etc., also don't change. Only the order in which heroes appear in the tavern changes. But let the experts correct me.
P.S.: The monsters will be the same because they are embedded in the map. But the spells in the guilds, utopias, crypts, and heroes in the taverns will all change! The most important thing is that the starting army changes drastically!!!
P.S.2: But, in my opinion, you can't click the "Replay Scenario" button in multiplayer. Correct me if I'm wrong.