So far, there are only 3 or 4 files I have ever had to deal with or dredge through, to find information:
(file extensions are .dbs for CoDS and .gld for Gold)1. savegame.dbs/gld - the current state of your characters and the world as they know it (i.e. what doors, chests, locks, grates have been opened, what events you have passed, choices you have made (i.e. paid or refused Barlone, who is dead (i.e. Mick, Ratsputin )
2. scenario.dbs/gld - the "template" - it holds all of the descriptions of the things pointed to in the saved game. For instance, whether you have opened a gorrors chest or not is in the saved game. What it has in it is in the scenario. The scenario also holds the detailed info on items, monsters adn spells.
3. messages.dbs/gld - just that, a list of all the messages you may see while playing (combat and npc dialog).
As for where the specific "map" information is held, I would guess it is in both the saved game and scenario and when you start a new game, you get a copy of the scenario map stuck into your saved game.
I am guessing your saved game map is what is corrupt. I have seen that happen in Wiz 7, where certain areas of the game just become inaccessible.
I think your only two viable options are to:
1. cut your party out of the corrupted game and paste them back into a previous saved game
2. figure out where the "map" section of a saved game is and fix it somehow
Maybe that is just one viable option
Tools for your Wizardry(r) toolkit