Thanks everyone. I'm very clear on the fact that unused (but connected) resources can disappear, and that connected resources can disappear--period. But it does indeed matter to my mod whether or not a tile that has an undiscovered resource could lose that resource (as a random event within the bounds of its disappearance probability) before the resource is discovered IF the tile has a road.
You see, my mod is an altered version of Rhye's of Civilization. It uses a world map for the scenario, in which all resources have been placed according to where those resources actually exist in real life. It has taken countless hours for me to research where the major deposits of Copper were in the ancient era, for example, or where current deposits of boron-containing compounds are mined (such as Borax). Some of these strategic resources won't appear on the map until the Space Age (the fourth era in my mod; I've compressed the Industrial and Modern eras together). So it would make a mess of my map if some of the resources that are supposed to appear late in the game (such as Boron and Titanium), get moved away from their historical locations before the game even gets to the Space Age.
In making Rhye's of Civilization, Rhye decided to remove all disappearance probabilities from the resources because it would create problems if some civs didn't get access to their intended resources. For example, if England lost its Coal, they wouldn't be able to become the industrial powerhouse that they were historically. Worse, Rhye has fine-tuned the map so that the highly industrialized European nations won't be overpowered (given their close proximity to one another, they trade techs more than do other civs on the map, and so they tend to be more advanced in the tech race). To counteract this tech advantage for European civs, Rhye has placed some handicapping "bonus" resources and landmark terrain on the map. For example, being close to Europe and having a lot of room to expand, Russia would be overpowered if it weren't for a lot of poor-quality landmark terrain that is placed in its vicinity. The mixture of resources, terrain, and available landspace for cities is finely tuned to keep some civs from having a guaranteed win. But a lot of the balance depends on the assumption that civs will have access to certain resources. Hence the decision to remove the disappearance probability values for strategic resources in the Rhye's of Civilization mod.
Then I come along. I want to expand the Rhye's of Civilization mod and allow for a space age. I wonder if rather than removing the disappearance probability values entirely, I could just double them--making them twice as un-likely to disappear as normal.
But I'm bothered by the possibility that a resource counts as being "present" on the map even if it isn't yet visible to a player. The AI players, for example, can always see where resources will later appear on the map, and choose their city locations accordingly.
Here's another take on the question. What if I can see a resource (say, Saltpeter) that is in my neighbor's empire. I have researched Gunpowder, so I can see where the resource will be. He hasn't yet researched Gunpowder, so the resource technically shouldn't be visible to him yet. But I can see it. And I can see that he has already built a road on that tile. Would it be possible for the resource to be exhausted in this case before my opponent researches Gunpowder?
Maybe I'll just have to do the same thing Rhye did, and make the strategic resources inexhaustable. But I'd prefer not to, because I think it is an important part of the game.
