On way or the other, I do not anticipate any major "story changes" in our campaign world because of the shift in rules. No matter what system we are using we will try to publish a setting that is true to the pulp fantasy roots of D&D, which is a surprisingly bendy set of influences.
If the 4e PH lacks a bard we will either avoid stories with bards until WotC gives us one or make one of our own that will suffice in the interregnum.
Of all the things that concern me about 4e, this is not one of them.
Actually, I'm not that concerned about 4e, and I'm really looking forward to it. A lot of the "sacred cows" issues have to do with elements of the game that have not traditionally been open and are unlikely to be open in the new edition.
I was initially bent out of shape about the changes to the Great Wheel and to the succubi, but Paizo can't really use the Great Wheel one way or the other, and we can easily include a "traditional" succubus in our stuff if we want to.
So I am not worried about the impact the 4e rules will have on our setting.
--Erik