You can get a replacement key using the procedure linked to in the
Inventory files topic. I'll have to load my save at the start of act 4 to get the key, and update that topic in awhile. When I do, save before the door, backup your inventory files, replace them with mine, reload the save, open the door, save again, and restore your backup inventory files to that new save.
There is also a way to edit your character's position (
Teleporting anywhere) or get through doors or walls, etc (
armory trick in act 1). However, it would be better to get the door open, so you can freely pass after that.
