That's such a difficult question, because Wicked might not be what it is today if the casting was different. So much of the "success" of Wicked has to do with the original cast, creating the material to suit their skills, how they interpreted the material, and the fanbase they had coming into the Broadway premiere. If Idina were out and Shoshana were in, everything would have been completely different. The "riffs" that Sho does would be expected instead of "extras." Some of the songs would potentially be in different keys or even completely different material. Who knows, it might have even bombed. The critics didn't really like the show, but all pretty much raved about what Idina and Kristen brought to the show. The chemistry might not have worked the same between Sho and Kristen and it could have been completely slammed by the critics.
Could have been better . . . like I said, it's difficult to say what would have happened.
Sorry, that went around in circles!!!
". . . POP . . ."