[Gorwingel]

That is an interesting question (or at least I find it interesting). Maybe the ring would have never been distroyed if Gandalf had made it all the way and never had fought the Balrog? I think though that Gandalf had probably some slight idea. But one question that I need answering... (please enlighten me) Had Gandalf visited Mordor before and was he familliar with the area? I know that he had traveled all over Middle Earth and was very familliar with many areas, but had he been there?
Because if he had never been (though I think he must have gone there at least once) then of course he would have had no idea, or just a little bit of an idea from the information he would have probably gotten from maps.
But I doubt that they would have made it all the way to Mt. Doom unoticed if they had had Gandalf with them. Sauron would probably most likely have had the sense to sense the power of a great and powerful wizard coming near to him.